



























































































































































































































































































































































































































































































































































































































































Class 

Book 



Copyright ^ 0 


COPYRIGHT DEPOSIT. 
























■ 















































ROAD CONSTRUCTION IN THE PHILIPPINES 

Section of 35-mile road built by American engineers, connecting the seaport, of Dagupan with 
the mountain village of Baguio, province of Benguet, island of Luzon, and affording a cool and 
healthful retreat from the heat and malaria of the lowland regions. Dagupan lies 120 miles north of 
Manila, with which it is connected by rail. This view reveals some of the engineering difficulties to 
be overcome, masonry and concrete work of the type shown being necessary at many points. 












Highway Construction 


A Practical Guide to 

MODERN METHODS OF ROADBUILDING AND THE DEVELOPMENT OF 

BETTER WAYS OF COMMUNICATION 


By AUSTIN T. BYRNE 

Civil Engineer. Author of “Highway Construction,” 
“ Materials and Workmanship” 


a?id 

ALFRED E. PHILLIPS, C.E., Ph.D. 

} 

Professor of Civil Engineering, Armour Institute of Technology 


ILLUSTRATED 




> D 


CHICAGO 

AMERICAN SCHOOL OF CORRESPONDENCE 

19 0 8 


> > 


I. 


LIBRARY of CONGRESS 
OntGooj Received 

ma;< 6 iyob 

Oo«r. »tru friury 

&dt '6 HfOj 
CU3&A AAc. no, 

' m \ s . 


Copyright 1907 by 

American School of Correspondence 

Entered at Stationers’ Hall, London 
All Rigiits Reserved 












Foreword 


« 



N recent-years, such marvelous advances have been 
made in the engineering and scientific fields, and 
so rapid has been .the evolution of mechanical and 
constructive processes and methods, that a distinct 
need has been, created for a series of practical 
working guides , of convenient size and low cost, embodying the 
accumulated results of experience and the most approved modern 
practice along a great variety of lines. To fill this acknowledged 
need, is the special purpose of the series of handbooks to which 


this volume belongs. 


«L In the preparation of this series, it has been the aim of the pub¬ 
lishers to lay special stress on the practical side of each subject, 
as distinguished from mere theoretical or academic discussion. 
Each volume is written by a well-known expert of acknowledged 
authority in his special line, and is based on a most careful study 
of practical needs and up-to-date methods as developed under the 
conditions of actual practice in the field, the shop, the mill, the 
power house, the drafting room, the engine room, etc. 


C, These volumes are especially adapted for purposes of self- 
instruction and home study. The utmost care has been used to 
bring the treatment of each subject within the range of the com- 




mon understanding, so that the work will appeal not only to the 
technically trained expert, but also to the beginner and the self- 
taught practical man who wishes to keep abreast of modern 
progress. The language is simple and clear; heavy technical terms 
and the formulae of the higher mathematics have been avoided, 
yet without sacrificing any of the requirements of practical 
instruction; the arrangement of matter is such as to carry the 
reader along by easy steps to complete mastery of each sub ject ; 
frequent examples for practice are given, to enable the reader to 
test his knowledge and make it a permanent possession; and the 
illustrations are selected with the greatest care to supplement and 
make clear the references in the text. 

«L The method adopted in the preparation of these volumes is that 
which the American School of Correspondence has developed and 
employed so successfully for many years. It is not an experiment, 
but has stood the severest of all tests—that of practical use—which 
has demonstrated it to be the best method yet devised for the 
education of the busy working man. 

«1 For purposes of ready reference and timely information when 
needed, it is believed that this series of handbooks will be found to 
meet every requirement. 








Table of Contents 


Country Roads .Page 1 

Object of Roads—Road Resistances to Traction—Axle Friction—Air- 
Resistance—Tractive Power and Gradients—Tractive Power of 
Horses—Effect of Springs on Vehicles—Location of Roads—Contour 
Lines—Levels—Cross-Levels—Bridge Sites—Mountain Roads—Align- 
- ment of Roads—Zigzags—Final Location—Construction Profile—De¬ 
termination of Gradients—Level Stretches—Width and Transverse 
Contour—Drainage—Side Ditches—Water Breaks—Culverts—Jointing 
of Pipe—Earthwork—Formation of Embankments—Roadways on 
Rock Slopes—Earth Roads—Sand Roads—Tools Used in Grading, 
Draining, etc.—Rollers—Sprinkling Carts—Road Coverings—Gravel 
Roads—Broken Stone (Macadam or Telford) Roads. 


* 

City Streets .Page 73 

General Arrangement—Width of Streets—Street Grades—Grades at 
Street Intersections—Transverse Grade-—Transverse Contour or Crown 
—Drainage—Gutters—Catch-Basins—Foundations for Pavements. 


Stone-Block Pavements .Page 82 

Properties of Stones (Granite, Sandstone, Trap Rock, Limestone) — 
Cobblestone Pavement—Belgian Block Pavement—Granite Block 
Pavements—Manner of Laying Blocks—Cushion Coat above Foun¬ 
dation—Ramming—Joint Filling. 


Brick and Wood Pavements .Page 92 

Requirements of Paving Brick—Tests of Paving Brick (Rattler, 
Absorption, Cross-Breaking, Crushing)—Properties of Paving Brick— 
Advantages and Defects of Brick Pavements—Foundation and Sand 
Cushion—Manner of Laying—Joint Filling—Tools—Concrete-Mixers— 
Gravel Heaters—Melting Furnaces—Wood Pavements—Kinds of Wood 
Used—Chemical Treatment of Wood (Creosoting)—Expansion of 
Blocks—Manner of Laying—Filling for Joints. 

Asphalt Pavements, Footpaths, Curbs, and Gutters . . Page 106 

Bituminous Limestone and Sandstone—Trinidad Asphaltum—Artificial 
Asphalt Pavements—Mixing Formula—Advantages and Defects— 
Asphalt Blocks—Asphalt Macadam—Tools—Footpaths—Curbstones— 
Artificial Stone—Problem of Pavement Selection—Resistance to Trac¬ 
tion on Various Pavements—Serviceability—Safety—Life of Pave¬ 
ments—Cost—Relative Economies. 


Index . 


Page 131 




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HIGHWAY CONSTRUCTION 


PART I. 


COUNTRY ROADS. 

GENERAL CONSIDERATIONS. 

Object of Roads. The object of ii road is to provide a way 
for the transportation of persons and goods from one place to another 
with the least expenditure of power and expense. The facility with 
which this traffic or transportation may be conducted over any given 
road depends upon the resistance offered to the movement of vehicles. 
This resistance is composed of: (1) The resistance offered by the 
roadway, which consists of (a) “friction” between the surface of 
the road and the wheel tires; (b) resistance offered to the rolling of 
the wheels, occasioned by the want of uniformity in the road surface, 
or lack of strength to resist the penetrating efforts of loaded wheels, 
thus requiring the load to be lifted over projecting points and out of 
hollows and ruts, thereby diminishing the effective load the horse 
may draw to such as it can lift. This resistance is called “resistance 
to rolling” or “penetration;” (c) resistance due to gravity called 
“grade resistance;” (2) The resistance offered bv vehicles, termed 
“axle friction;” (3) Resistance of the air. 

The road which offers the least resistance to traffic should com¬ 
bine a surface on which the friction of the wheels is reduced to the 
least possible amount, while offering a good foothold for horses, to 
enable them to exert their utmost tractive power, and should be so 
located as to give the most direct route with the least gradients. 

Friction. The resistance of friction arises from the rubbing of 
the wheel tires against the surface of the road. This resistance to 
traction is variable, and can be determined only by experiment. 
From many experiments the following deductions are drawn: 

(1) The resistance to traction is directly proportional to the 
pressure. 


2 


HIGHWAY CONSTRUCTION 


(2) On solid, unyielding surfaces it is independent of the width 
of the tire, but on compressible surfaces the resistance decreases as 
the width of the tire increases (but there is no material advantage 
gained in making a tire more than 4 inches wide). 

(3) It is independent of the speed. 

(4) On rough, irregular surfaces, which give rise to constant 
concussion, it increases with the speed. 

The following table shows the relative resistance to traction of 
various surfaces: 

TABLE 1. 

Resistance to Traction on Different Road Surfaces. 


Traction Resistance. 



Pounds per ton. 

In terms of load. 

Earth road—-ordinary condition. 

Gravel. 

Sand. 

Macadam. 

Plank Road. 

Steel Wheelway. 

50 to 200 

50 to 100 

100 to 200 

30 to 100 

30 to 50 

15 to 40 

1 to ^ 

4T lU 10 

1 to 1 . 

To tu 2 0 

1 to 1 
"2 0 XO TO 

1 to 1 

TT x() -go 

1_ to 1 

17 U) Tff 

_1 _ to _J_ 

13 3 5 0 

These coefficients refer to the 

power required to keep the load 


in motion. It requires from two to six or eight times as much force 
to start a load as it does to keep it in motion, at two or three miles 
per hour. The extra force required to start a load is due in part 
to the fact that during the stop the wheel may settle into the road 
surface, in part to the fact that the axle friction at starting is greater 
than after motion has begun, and further in part to the fact that 
energy is consumed in accelerating the load. 

Resistance to Rolling. This resistance is caused (1) by the 
wheel penetrating or sinking below the surface of the road, leaving 
a track or rut behind it. It is equal to the product of the load mul¬ 
tiplied by one-third of the semi-chord of the submerged arc of the 
wheel; and (2) by the wheel striking or colliding with loose or pro¬ 
jecting stones, which give a sudden check to the horses, depending 
upon the height of the obstacle, the momentum destroyed being 
oftentimes considerable. 

The rolling resistance varies inversely as some function of the 






























HIGHWAY CONSTRUCTION 


3 


diameter of the wheel, as the larger the wheel the less force required 
to lift it over the obstruction or to roll it up the inclination due to the 
indentation of the surface. 

1 he power required to draw a wheel over a stone or any ob¬ 
stacle, such as S in Fig. 1, may be tluis calculated. Let P represent 
the power sought, or that which would just balance the weight on 

the point of the stone, and the 
slightest increase of which 
would draw it over. This 
power acts in the direction 
C P with the leverage of B C 
or I) E. Gravity, represented 
by W, resists in the direction 
C B with the leverage B D. 
The equation of equilibrium 
will be P X C B = AY X B D, whence 



B D 1 C D 2 - B C 2 
P = W _ w 

CB CD -AD 


Let the radius of the wheel = CD = 26 inches, and the height 
of the obstacle = AB = 4 inches. Let the weight W = 500 pounds, 
of which 200 pounds may be the weight of the wheel and 300 pounds 
the load on the axle. The formula then becomes 


V 676 -484 13.85 

P = 500 — 500 9Q = 314.7 pounds. 


The pressure at the point 1) is compounded of the weight and 
the power, and equals 

CD 26 r 

W g-g = 500 X 22 = 591 pounds, 

and therefore acts with this great effect to destroy the road in its 
collision with the stone, in addition there is to be considered the 
effect of the blow given by the wheel in descending from it. For 
minute accuracy the non-horizontal direction of the draught and 
the thickness of the axle should be taken into account. The power 
required is lessened by proper springs to vehicles, by enlarged wheels, 
and by making the line of draught ascending. 









4 


HIGHWAY CONSTRUCTION 


The mechanical advantage of the wheel in surmounting an 
obstacle may be computed from the principle of the lever. 

Let the wheel. Fig. 2, touch the horizontal line of traction in 
the point A and meet a protuberance B D. Suppose the line of 
draught C P to be parallel to AB. Join C D and draw the perpen¬ 
diculars D E and D F. We 
may suppose the power to be 
applied at E and the weight at 
F, and the action is then the 
p same as the bent lever E I) F 
turning round the fulcrum at 
1). Hence P : W :: F D : D E. 

_ But FD : D E ::tanFCD:l, 

B and tan F C D = tan 2 

(DAB); therefore P = W 
tan 2 (DAB). Now it is obvious that the angle DAB increases 
as the radius of the circle diminishes; and therefore, the weight W 
being constant, the power required to overcome an obstacle of given 
height is diminished when the diameter is increased. Large wheels 
are therefore the best adapted for surmounting inequalities of the 
road. 

There are, however, circumstances which provide limits to the 
height of the wheels of vehicles. If the radius A C exceeds the 
height of that part of the horse to which the traces are attached, 
the line of traction C P will be inclined to the horse, and part of the 
power will be exerted in pressing the wheel against the ground. The 
best average size of wheels is considered to be about 6 feet in diameter. 

Wheels of large diameter do less damage to a road than small 
ones, and cause less draught for the horses. 

With the same load, a two-wheeled cart does far more damage 

o 

than one with four wheels, and this because of their sudden and 
irregular twisting motion in the trackway. 

Grade Resistance is due to the action of gravity, and is the 
same on good and bad roads. On level roads its effect is immaterial, 
as it acts in a direction perpendicular to the plane of the horizon, and 
neither accelerates nor retards motion. On inclined roads it offers 
considerable resistance, proportional to the steepness of the incline. 









HIGHWAY CONSTRUCTION 


The resistance due to gravity on any incline in pounds per ton 

. 2000 

is equal to . ..—• 

rateoi grade 

The following table shows the resistance due to gravity on dif¬ 
ferent grades. 

TABLE 2. 

Resistance Due to Gravity on Different Inclinations. 


Grade 1 in . .. 20 30 40 50 60 70 80 90 100 200 300 400 

Rise in feet per mile . . .264 176 132 105 88 75 66 58 52 26 17 13 

Resistance in lb. per ton .112 744 56 45 38 32 28 25 22 11^ 74 54 

The additional resistance caused by inclines may be investigated 

in the following manner: Suppose the whole weight to be borne on 
one pair of wheels, and that the tractive force is applied in a direction 
parallel to the surface of the road. 

Let A B in Fig. 3 represent a portion of the inclined road, C 
being a vehicle just sustained in its position by a force acting in the 
direction C D. It is evident that the vehicle is kept in its position 
by three forces; namely, by its own weight W acting in the vertical 
direction C F, by the force F applied in the direction C D parallel 
to the surface of the road, and by the pressure P which the vehicle 
exerts against the surface of the road acting in the direction C E 

perpendicular to same. To 
determine the relative magni¬ 
tude of these three forces, 
draw a horizontal line A G 
and the vertical one B G; 
then, since the two lines C F 
and B G are parallel and 
are both cut by the line AB, 
they must make the two 
angles C F E and A B G 
equal; also the two angles C E F and A G B are equal; therefore, the 
remaining angles F C E and B A G are equal, and tl\e two triangles 
C F E and A B G are similar. And as the three sides of the former 
are proportional to the three forces by which the vehicle is sustained, 
so also are the three sides of the latter; namely, AB or the length 
of the road is proportional to W, or the weight of the vehicle; B G, 












HIGHWAY CONSTRUCTION 


6 


or the vertical rise in the same, to F, or the force required to sustain 
the vehicle on the incline; and AG, or the horizontal distance in 
which the rise occurs, to P, or the force with which the vehicle presses 
upon the surface of the road. T herefore, 

W : A B : : F : G B, 

and 

W : A B : : P : A G. 

If to A G such a value he assigned that the vertical rise of the 
road is exactly one foot, then 

W 


F = 


and 


P = 


w 

A B - 

W • A G 
AB 


AGA 1 

WAG 
V A G 3 + \ 


= W • sin A 


= W • cos A, 


in which A is the angle B A G. 

To find the force requisite to sustain a vehicle upon an inclined 
road (the effects of friction being neglected), divide the weight of the 
vehicle and its load by the inclined length of the road, the vertical 
rise of which is one foot, and the quotient is the force required. 

To find the pressure of a vehicle against the surface of an inclined 
road, multiply the weight of the loaded vehicle by the horizontal 
length of the road, and divide the product by the inclined length of 
the same; the quotient is the pressure required. 

The force with which a vehicle presses upon an inclined road 
is always less than its actual weight; the difference is so small that, 
unless the inclination is very steep, it may be taken equal to the 
weight of the loaded vehicle. 

To find the resistance to traction in passing up or down an 
incline, ascertain the resistance on a level road having the same surface 
as the incline, to which add, if the vehicle ascends, or subtract, if 
it descends, the force requisite to sustain it on the incline; the sum 
or difference, as the case may be, will express the resistance. 

Tractive Power and Gradients. The neeessitv for easv 

«/ 

grades is dependent upon the power of the horse to overcome the 
resistance to motion composed of the four forces, friction, collision, 
gravity, and the resistance of the air. 

All estimates on the tractive power of horses must to a certain 







HIGHWAY CONSTRUCTION 


7 


extent he vague, owing to the different strengths and speeds of animals 
of the same kind, as well as to the extent of their training to any 
particular kind of work. 

The draught or pull which a good average horse, weighing 1,200 
pounds, can exert on a level, smooth road at a speed of 2\ miles per 
hour is 100 pounds, equivalent to 22,000 foot-pounds per minute, 
or 13,200,000 foot-pounds per day of 10 hours. 

The tractive power diminishes as the speed increases and, per¬ 
haps, within certain limits, say froyn f to 4 miles per hour, nearly 
in inverse proportion to it. Thus the average tractive force of a 
horse, on a level, and actually pulling for 10 hours, may he assumed 
approximately as follows: 

TABLE 3. 

Tractive Power of Horses at Different Velocities. 


Miles per hour. 

Tractive 
Force. Lb. 

Miles per hour. 

Tractive 
Force. Lb. 

4. 

333.33 

91 

Ill 11 

1 . 

250 

~ 4 . 

91 

1 00 

11. 

200 

Ai . 

90 91 

H . 

166.66 

4 . 

3 . 

83 33 

if . 

142.86 

34. 

71 .43 

■1 

125 

4 . 

62.50 





The work done by a horse is greatest when the velocity with 
which he moves is J of the greatest velocity with which he can move 
when unloaded; and the force thus exerted is 0.45 of the utmost 
force that he can exert at a dead pull. 

The traction power of a horse may he increased in about the 
same proportion as the time is diminished, so that when working 
from 5 to 10 hours, on a level, it will he about as shown in the following 
table: 

TABLE 4. 

Hours per day Traction (pounds) Hours per day Traction (pounds) 

10 . 100 7 . 146f 

9 . 114 6 166J 

8 . 125' 5 . 200 

The tractive power of teams is about as follows 

1 horse . =1 

2 horses . 0.95 X 2 = 1.90 

3 “ . 0.85 X 3 = 2.55 

4 “ . 0.80X4 ='3.20 












































8 


HIGHWAY CONSTRUCTION 


Loss of Tractive Power on Inclines. In ascending in¬ 
clines a horse’s power diminishes rapidly; a large portion of his 
strength is expended in overcoming the resistance of gravity due to 
his own weight and that of the load. Table 5 shows that as the 
steepness of the grade increases the efficiency of both the horse and 
the road surface diminishes; that the more of the horse’s energy is 
expended in overcoming gravity the less remains to overcome the 
surface resistance. 

TABLE 5. 

Effects of Grades Upon the Load a Horse can Draw on Different 

Pavements. 


Grade. 

Earth. 

Broken Stone. 

Stone Blocks. 

Asphalt. 

Level 


1.00 

1 .00 

1.00 

1.00 

1 

: 100 

.80 

.66 

.72 

.41 

2 

: 100 

.66 

.50 

.55 

.25 

3 

: 100 

.55 

.40 

.44 

.18 

4 

: 100 

.47 

.33 

.36 

.13 

5 

: 100 

.41 

.29 

.30 

.10 

10 

: 1 00 

.26 

.16 

.14 

.04 

15 

100 

.10 

.05 

.07 


20 

100 

.04 

. . . 

.03 



Table 6 shows the gross load which an average horse, weighing 
1,200 pounds, can draw on different kinds of road surfaces, on a 
level and on grades rising five and ten feet per one hundred feet. 


table 6. 


Description of Surface. 

Level. 

5 per cent 
grade. 

10 per cent 
grade. 

Asphalt. 

13,216 



Broken stone (best condition). 

6,700 

i,840 

1,060 

“ “ (slightly muddy). 

4,700 

1,500 

1,000 

“ “ (ruts and mud). 

3,000 

1,390 

890 

(very bad condition) . . 

1,840 

1,040 

740 

Earth (best condition). 

3,600 

1,500 

930 

“ (average condition).... 

1,400 

900 

660 

“ (moist but not muddy). 

1,100 

780 

600 

Stone-block pavement (dry and clean) 

8,300 

1,920 

1,090 

“ “ “ (muddy). 

6,250 

1,800 

1,040 

Sand (wet). 

1,500 

675 

390 

“ (dry)... 

• 

1,087 

445 

217 


The decrease in the load which a horse can draw upon an incline 
is not due alone to gravity; it varies with the amount of foothold 















































HIGHWAY CONSTRUCTION 


9 


afforded by the road surface. The tangent of the angle of inclination 
should not be greater than the coefficient of fractional resistance; 
therefore it is evident that the smoother the road surface, the easier 
should be the grade. The smoother the surface the less the foothold, 
and consequently the load. 

The loss of tractive power on inclines is greater than any inves¬ 
tigation will show; for, besides the increase of draught caused by 
gravity, the power of the horse is much diminished by fatigue upon 
a long ascent, and even in greater ratio than man, owing to its anatom¬ 
ical formation and great weight. Though a horse on a level is as 
strong as five men, on a grade of 15 per cent, it is less strong than 
three; for three men carrying each 100 pounds will ascend such a 
grade faster and with less fatigue than a horse with 300 pounds. 

A horse can exert for a short time twice the average tractive 
pull which he can exert continuously throughout the day’s work; 
hence, so long as the resistance on the incline is not more than double 
the resistance on the level, the horse will' be able to take up the full 
load which he is capable of drawing. 

Steep grades are thus seen to be objectionable, and particularly 
so 'when a single one occurs on an otherwise comparatively level road, 
in which case the load carried over the less inclined portions must 
be reduced to what can be hauled up the steeper portion. 

The bad effects of steep grades are especially felt in winter, 
when ice covers the roads, for the slippery condition of the surface 
causes danger in descending, as well as increased labor in ascending; 
the water of rains also runs down the road and gulleys it out, destroy¬ 
ing its surface, thus causing a constant expense for repairs. The 
inclined portions are subject to greater wear from horses ascending, 
thus requiring thicker covering than the more level portions, and 
hence increasing the cost of construction. 

It will rarely be possible, except in a flat or comparatively level 
country, to combine easy grades with the best and most direct route. 
These two requirements will often conflict. In such a case, increase 
the length. The proportion of this increase will depend upon the 
friction of the covering adopted. But no general rule can be given 
to meet all cases as respects the length which may thus be added, 
for the comparative time occupied in making the journey forms an 





10 


HIGHWAY CONSTRUCTION 


important element in any case which arises for settlement. Disre¬ 
garding time, the horizontal length of a road may be increased to 
avoid a 5 per cent grade, seventy times the height. 

Table 7 shows, for most practical purposes, the force required 
to draw loaded vehicles over inclined roads. The first column ex¬ 
presses the rate of inclination; the second, the pressure on the plane 
in pounds per ton; the third, the tendency down the plane (or force 
required to overcome the effect of gravity) in pounds per ton; the 
fourth, the force required to haul one ton up the incline; the fifth, the 
length of level road which would be equivalent to a mile in length of 
the inclined road—that is, the length which would require the same 
motive power to be expended in drawing the load over it, as would 
be necessary to draw over a mile of the inclined road; the sixth, the 
maximum load which an average horse weighing 1,200 pounds can 
draw over such inclines, the friction of the surface being taken at 
^ of the load drawn. 

TABLE 7. 


Rate of grade. 
Feet per 100 
feet. 

Pressure on 
the plane in 
lb. per ton. 

Tendency 
down the 
plane in lb. 
per ton. 

Power in lb. 
required to 
haul one ton 
up the plane. 

Equivalent 
length of level 
road. Miles. 

Maximum 
load in lb. 
which a hoi’se 
can haul. 

0.0 

2240 

.00 

45.00 

1.000 

6270 

0.25 

2240 

5.60 

50.60 

1.121 

5376 

0.50 

2240 

11.20 

56.20 

1.242 

4973 

0.75 

2240 

16.80 

61.80 

1.373 

4490 

1. 

2240 

22.40 

67.40 

1.500 

4145 

1.25 

*2240 

28.00 

73.00 

1.622 

3830 

1.50 

2240 

33.60 

78.60 

1.746 

3584 

1.75 

2240 

39.20 

84.20 

1.871 

3290 

2 

2240 

45.00 

90.00 

2.000 

3114 

2.25 

2240 

50.40 

95.40 

2.120 

2935 

2.50 

2240 

56.00 

101.00 

2.244 

2725 

2.75 

2240 

61.33 

106.33 

2.363 

2620 

3 

2239 

67.20 

112.20 

2.484 

2486 

4 

2238 

89.20 

134.20 

2.982 

2083 

5 

2237 

112.00 

157.00 

3.444 

1800 

6 

2233 

134.40 

179.40 

3.986 

1568 

7 

2232 

156.80 

201.80 

4.844 

1367 

8 

2232 

179.20 

224.20 

4.982 

1235 

9 

2231 

201.60 

246.60 

5.840 

1125 

10 

2229 

224.00 

269.00 

5.977 

1030 


* Near enough for practice; actually 2239.888. 

Pressure on the plane = weight x nat cos of angle of plane. 


Axle Friction. The resistance of the hub to turning on the 
axle is the same as that of a journal revolving in its bearing, and has 
























HIGHWAY CONSTRUCTION 


11 


nothing to do with the condition of the road surface. The coefficient 
of journal friction varies with the material of the journal and its 
bearing, and with the lubricant. It is nearly independent of the 
velocity, and seems to vary about inversely as the square root of the 
pressure. For light carriages when loaded, the coefficient of friction 
is about 0.020 of the weight on the axle; for the ordinary thimble- 
skein wagon when loaded, it is about 0.012. These coefficients are 
for good lubrication; if the lubrication is deficient, the axle friction 
is two to six times as much as above. 

The traction power required to overcome the above axle friction 
for carriages of the usual proportions is about 3 to 3J lb. per ton of 
the weight on the axle; and for truck wagons, which have medium 
sized wheels and axles, is about 3J to 4J lb. per ton. 

Resistance of the Air. The resistance arising from the 
force of the wind will vary with the velocity of the wind, with the 
velocity of the vehicle, with the area of the surface acted upon, and 
also with the angle of incidence of direction of the wind with the 
plane of the surface. 

The following table gives the force per square foot for various 
velocities: 

TABLE 8. 


Velocity of wind in miles 
per hour. 

Force in lbs. per sq. ft. 

Description. 

15 

1.107 

Pleasant Breeze 

20 

25 

1.968 \ 

3.075 / 

Brisk Gale 

30 

35 

4.4281 

6.027 / 

High Wind 

40 

45 

7.872 l 

9.963 ^ 

Very High Wind 

50 

12.300 

Storm 


Effect of Springs on Vehicles. Experiments have shown 
that vehicles mounted on springs materially decrease the resistance to 
traction, and diminish the wear of the road, especially at speeds 
beyond a walking pace. Going at a trot, they were found not to 
cause more wear than vehicles without springs at a walk, all other 
conditions being similar. Vehicles with springs improperly fixed 
cause considerable concussion, which in turn destroys the road 
covering. 
















V2 


HIGHWAY CONSTRUCTION 


LOCATION OF COUNTRY ROADS, 

The considerations governing the location of country roads are 
dependent upon the commercial condition of the country to be 
traversed. In old and long-inhabited sections the controlling ele¬ 
ments will be the character of the traffic to be accommodated. In 
such a section, the route is generally predetermined, and therefore 
there is less liberty of a choice and selection than in a new and sparsely 
settled district, where the object is to establish the easiest, shortest, 
and most economical line of intercommunication according to the 
physical character of the ground. 

Whichever of these two cases may have to be dealt with, the same 
principle governs the engineer, namely, to so lay out the road as to 
effect the conveyance of the traffic with the least expenditure of 
motive power consistent with ‘economy of construction and main¬ 
tenance. 

Economy of motive power is promoted by easy grades, by the 
avoidance of all unnecessary ascents and descents, and by a direct 
line; but directness must be sacrificed to secure easy grades and to 
avoid expensive construction. 

Reconnoissance. The selection of the best route demands 
much care and consideration on the part of the engineer. To obtain 
the requisite data upon which to form his judgment, he must make 
a personal reconnoissance of the district. This requires that the 
proposed route be either ridden or walked over and a careful examina¬ 
tion made of the principal physical contours and natural features of 
the district. The amount of care demanded and the difficulties 
attending the operations will altogether depend upon the character 
of the country. 

The immediate object of the reconnoissance is to select one or 
more trial lines, from which the final route may be ultimately deter¬ 
mined. 

When there are no maps of the section traversed, or when those 
which can be- procured are indefinite or inaccurate, the work of 
reconnoitering will be much increased. 

In making a reconnoissance tlierfc are several points which, if 
carefully attended to, will very considerably lessen the labor and 
time otherwise required. Lines which would run along the imme- 



HIGHWAY CONSTRUCTION 


13 


diate bank of a large stream must of necessity intersect all the tribu¬ 
taries confluent on that bank, thereby demanding a corresponding 
number of bridges. Those, again, which are situated along the 
slopes of hills are more liable in rainy weather to suffer from washing 
away of the earthwork and sliding of the embankments; the others 
which are placed in valleys or elevated plateaux, when the line crosses 
the ridges dividing the principal water courses will have steep ascents 
and descents. 

In making an examination of a tract of country, the first point 
to attract notice is the unevenness or undulations of its surface, which 
appears to be entirely without system, order, or arrangement; but 
upon closer examination it will be perceived that one general prin¬ 
ciple of configuration obtains even in the most irregular countries. 
The country is intersected in various directions by main water courses 
or rivers, which increase in size as they approach the point of their 
discharge. Towards these main rivers lesser rivers approach on 
both sides, running right and left through the country, and into these, 
again, enter still smaller streams and brooks. The streams thus 
divide the hills into branches or spurs having approximately the same 
direction as themselves, and the ground falls in every direction from 
the main chain of hills towards the water courses, forming ridges 
more or less elevated. 

The main ridge is cut down at the heads of the streams into 
depressions called gaps or passes; the more elevated points are called 
peaks. The water which has fallen upon these peaks is the origin 
of the streams which have hollowed out the valleys. Furthermore, 
the ground falls in every direction towards the natural water courses, 
forming ridges more or less elevated running between them and 
separating from each other the districts drained by the streams. 

The natural water courses mark not only the lowest lines, but 
the lines of the greatest longitudinal slope in the valleys through which 
they flow. 

The direction and position of the principal streams give also 
the direction and approximate position of the high ground or ridges 
which lie between them. 

The positions of the tributaries to the larger stream generally 
indicate the points of greatest depression in the summits of the ridges, 







14 


HIGHWAY CONSTRUCTION 



Fig. 4. Contour Lines. 















































HIGHWAY CONSTRUCTION 


15 


and therefore the points at which lateral communication across the 
high ground separating contiguous valleys can be most readily made. 

The instruments employed in reconnoitering, are: The compass, 
for ascertaining the direction; the aneroid barometer, to fix the ap¬ 
proximate elevation of summits, etc.; and the hand level, to ascertain 
the elevation of neighboring points. If a vehicle can be used, an 
odometer may be added, but distances can usually be guessed or 
ascertained by time estimates or otherwise, closely enough for pre¬ 
liminary purposes. The best maps obtainable and traveling com¬ 
panions who possess a local knowledge of the country, together with 
the above outfit is all that will be necessary for the first inspection. 

The reconnoissance being completed, instrumental surveys of 
the routes deemed most advantageous should be made. When the 
several lines are plotted to the same scale, a good map can be pre¬ 
pared from which the exact location of the road can be determined. 

In making the preliminary surveys the topographical features 
should be noted for a convenient distance to the right and the left of 
the line, and all prominent points located by compass bearings. The 
following data should also be obtained: the importance, magnitude, 
and direction of all streams and roads crossed; the character of the 
material to be excavated or available for embankments, the position 
of quarries and gravel pits, and the modes of access thereto; and all 
other information that may effect a selection. 

Topography. There are various methods of delineating upon 
paper the irregularities of the surface of the ground. The method 
of most utility to the engineer is that by means of “contour lines.” 
These are fine lines traced through the points of equal level over the 
surface surveyed, and denote that the level of the ground throughout 
the whole of their course is identical; that is to say, that every part 
of the ground over which the line passes is at a certain height above 
a known fixed point termed the datum, this height being indicated 
by the figures written against the line. 

The intervals between the lines vertically are equal and may 
be 1, 3, 5, 10 or more feet apart; where the surface is very steep they 
lie close together. These lines by their greater or less distance apart 
have the effect of shading, and make apparent to the eye, the 
undulations and irregularities in the surface of the country. 




16 


HIGHWAY CONSTRUCTION 


60.00 


ro-55.00 

O 


54.20 


- 54.4- 



- 54.62 


Fig. 4 shows an imaginary tract of country, the physical features 
of which are shown by contour lines. 

Map. The map should show the 
lengths and direction of the different por¬ 
tions of the line, the topography, rivers, 
water courses, roads, railroads, and other 
matters of interest, such as town and 
county lines, dividing lines between property, 
timbered and cultivated lands, etc. 

Any convenient scale may be adopted; 

400 feet to an inch will be found the most 
useful. 

Memoir. The descriptive memoir 
should give with minuteness all information, 
such as the nature of the soil, character of 
the several excavations whether earth or 
rock, and such particular features as can¬ 
not be clearly shown upon the map or 
profile. 

Special information should be given re¬ 
garding the rivers crossed, as to their width, 
depth at highest known flood, velocity of 
current, character of banks and bottom, 
and the angle of skew which the course 
makes with the line of the road. 

Levels. Levels should be taken along 
the course of each line, usually at every 100 
feet, or at closer intervals, depending upon 
the nature of the country. 

In taking the levels, the heights of 
all existing roads, railroads, rivers, or 
canals should be noted. “ Bench marks ” 
should be established at least every half 
mile, that is, marks made on any fixed 
object, such as a gate post, side of a house, 
or, in the absence of these, a cut made 
on a large tree. The height and exact 


o) 53.a 



% 


— 54.80 




X 


•55.10—1/s 

' X 


oo 


-55.00- 




Fig. 5. Preliminary Profile 











HIGHWAY CONSTRUCTION 


17 


description of each bench mark should be recorded in the level book. 

Cross Levels. Wherever considered necessary levels at right 
angle to the center line should be taken. These will be found useful 
in showing what effect a deviation to the right or left of the surveyed 
line would have. Cross levels should be taken at the intersection of 
all roads and railroads to show to what extent, if any, these levels 
will have to be altered to suit the levels of the proposed road. 

Profile. A profile is a longitudinal section of the route, made 
from the levels. Its horizontal scale should be the same as that of 
the map; the vertical scale should be such as will show with distinct¬ 
ness the inequalities of the ground. 

Fig. 5 shows the manner in which a profile is drawn and the 
nature of the information to be given upon it. 

Bridge Sites, The question of choosing the site of bridges is 
an important one. If the selection is not restricted to a particular 
point, the river should be examined for a considerable distance above 
and below what would be the most convenient point for crossing; and 
if a better site is found, the line of the road must be made subordinate 
to it. If several practicable crossings exist, they must be carefully 
compared in order to select the one most advantageous. The follow¬ 
ing are controlling conditions: (1) Good character of the river bed, 
affording a firm foundation. If rock is present near the surface of 
the river bed, the foundation will be easy of execution and stability 
and economy will be insured. (2) Stability of river banks, thus 
securing a permanent concentration of the waters in the same bed. 
(3) The axis of the bridge should be at right angles to the direction 
of the current. (4) Bends in rivers are not suitable localities and 
should be avoided if possible. A straight reach above the bridge 
should be secured if possible. 

Final Selection. In making the final selection the following 
principles should be observed as far as practicable. 

(a) To follow that route which affords the easiest grades. The 
easiest grade for a given road will depend on the kind of covering 
adopted for its surface. 

(b) To connect the places by the shortest and most direct route 
commensurate with easy grades. 

. (c) To avoid all unnecessary ascents and descents. When a 






18 


HIGHWAY CONSTRUCTION 


road is encumbered with useless ascents, the wasteful expenditure of 
power is considerable. 

(i d ) To give the center line such a position, with reference to 
the natural surface of the ground, that the cost of construction shall 
be reduced to the smallest possible amount. 

(e) To cross all obstacles (where structures are necessary) as 
nearly as possible at right angles. The cost of skew structures 
increases nearly as the square of the secant of the obliquity. 

(/) To cross ridges through the lowest pass which occurs. 

(g) To cross either under or over railroads; for grade crossings 
mean danger to every user of the highway. 

Examples of Cases to be Treated. In laying out the line 
of a road, there are three cases which mav have to be treated, and 
each of these is exemplified in the contour map, Fig. 4. First, the 
two places to be connected, as the towns A and B on the plan, may 
be both situated in the same valley, and upon the same side of it; that 
is, they are not separated from each other by the main stream which 
drains the valley. This is the simplest case. Secondly, although 
both in the same valley, the two places may be on opposite sides of 
the valley, as at A and C, being separated by the main river. Thirdly, 
they may be situated in different valleys, separated by an intervening 
ridge of ground more or less elevated, as at A and D. In laying out 
an extensive line of road, it frequently happens that all these cases 
have to be dealt with. 

The most perfect road is that of which the course is perfectly 
straight and the surface practically level; and, all other things being 
the same, the best road is that which answers nearest to this de¬ 
scription. 

Now, in the first case, that of the two towns situated on the 
same side of the main valley, there are two methods which may be 
pursued in forming a communication between them. A road follow¬ 
ing the direct line between them, shown by the thick dotted line A B, 
may be made, or a line may be adopted which will gradually and 
equally incline from one town to another, supposing them to be at 
different levels; or, if they are on the same level, the line should keep 
at that level throughout its entire course, following all the sinuosities 
and curves which the irregular formation of the country may render 





HIGHWAY CONSTRUCTION 


19 


necessary for the fulfillment of these conditions. According to the 
first method, a level or uniformly inclined road might be made from 
one to the other; this line would cross all the valleys and streams 
which run down to the main river, thus necessitating deep cuttings, 
heavy embankments, and numerous bridges; or these expensive 
. works might be avoided by following the sinuosities of the valley. 
When the sides of the main valley are pierced by numerous ravines 
with projecting spurs and ridges intervening, instead of following the 
sinuosities, it will be found better to make a nearly straight line 
cutting through the projecting points in such a way that the material 
excavated should be just sufficient to fill the hollows. 

Of all these, the best is the straight or uniformly inclined, or 
level road, although at the same time it is the most expensive. If 
the importance of the traffic passing between the places is not suffi¬ 
cient to warrant so great an outlay, it will become a matter of consider¬ 
ation whether the course of the road should be kept straight, its surface 
being made to undulate with the natural face of the country; or 
whether, a level or equally inclined line being adopted, the course 
of the road should be made to deviate from the direct line, and follow 
the winding course which such a condition is supposed to necessitate. 

In the second case, that of two places situated on opposite sides 
of the same valley, there is, in like manner, the choice of a perfectly 
straight line to connect them, which would probably require a big 
embankment if the road was kept level, or steep inclines if it followed 
the surface of the country; or by winding the road, it may be carried 
across the valley at a higher point, where, if the level road be taken, 
the embankment would not be so high, or, if kept on the surface, 
the inclination would be reduced. 

In the third case, there is, in like manner, the alternative of 
carrying the road across the intervening ridge in a perfectly straight 
line, or of deviating it to the right and left, and crossing the ridge 
at a point where the elevation is less. 

The proper determination of the question which of these courses 
.is the best under certain circumstances involves a consideration of 
the comparative advantages and disadvantages of inclines and 
curves. What additional increase in the length of a road would be 
equivalent to a given inclined plane upon it; or conversely, what 




20 


HIGHWAY CONSTRUCTION 


inclination might be given to a road as an equivalent to a given de¬ 
crease in its length? To satisfy this question, the comparative force 
required to draw different vehicles with given loads must be known, 
both upon level and variously inclined roads. 

The route which will give the most general satisfaction consists 
in following the valleys as much as possible and rising afterward by 
gentle grades. This course traverses the cultivated lands, regions 
studded with farmhouses and factories. The value of such a line 
is much more considerable than that of a route by the ridges. The 
water courses which flow down to the main valley are, it is true, 
crossed where they are the largest and require works of large dimen¬ 
sions, but also they are fewer in number. 

Intermediate Towns. Suppose that it is desired to form a 
road between two distant towns, A and B, Fig. 6, and let us for the 
present neglect altogether the consideration of the physical features 
of the intervening country, assuming that it is equally favorable ' 
whichever line we select. Now at first sight, it would appear that 
under such circumstances a perfectly straight line drawn from one 

town to the other woidd be 
the best that could be chos¬ 
en. On more careful exam¬ 
ination however, of the lo¬ 
cality, we may find that 
there is a third town, C, 
situated somewhat on one 
side of the straight line 
which we have drawn from A to B; and although our primary object 
is to connect only the two latter, that it would nevertheless be of 
considerable service if the whole of the three towns were put into 
mutual connection with each other. 

This may be effected in three different ways, any one of which 
might, under the circumstances, be the best. In the first place, we 
might, as originally suggested, form a straight road from A to B, 
and in a similar manner two other straight roads from A to C, and 
from B to C, and this would be the most perfect way of effecting the 
object in view the distance between any of the two towns being 
reduced to the least possible. It would, however, be attended with 


c 

.St¬ 


s' 








/ 




\ 


\ 


s 


N 


D 

Fig. 6. 


B 






HIGHWAY CONSTRUCTION 


21 


considerable expense, and it would be requisite to construct a much 
greater length of road than according to the second plan, which would 
be to form, as before, a straight road from A to B, and from C to con¬ 
struct a road which should join the former at a point D, so as to be per¬ 
pendicular to it. The traffic between A or B and C would proceed to 
the point D and then turn off to C. With this arrangement, while 
the length of the roads would be very materially decreased, only a 
slight increase would be occasioned in the distance between C and 
the other two towns. The third method would be to form only the 
two roads A C and C B, in which case the distance between A and B 
would be somewhat increased, while that between A C or B and C 
would be diminished, and the total length of road to be constructed 
would also be lessened. 

As a general rule it may be taken that the last of these methods 
is the best and most convenient for the public; that is to say, that 
if the physical character of the country does not determine the course 
of the road, it will generally be found best not to adopt a perfectly 
straight line, but to vary the line so as to pass through all the prin¬ 
cipal towns near its general course. 

ITountain Roads. The location of roads in mountainous 
countries presents greater difficulties than in an ordinary undulating 
country; the same latitude in adopting undulating grades and choice 
of position is not permissible, for the maximum must be kept before 
the eve perpetually. A mountain road has to be constructed on the 
maximum grade or at grades closely approximating it, and but one 
fixed point can be obtained before commencing the survey, and that 
is the lowest pass in the mountain range; from this point the survey 
must be commenced. The reason for this is that the lower slopes 
of the mountain are flatter than those at their summit; they cover a 
larger area, and merge into the valley in diverse undulations. So 
that a road at a foot of a mountain may be carried at will in the 
desired direction by more than one route, while at the top of a moun¬ 
tain range any deviation from the lowest pass involves increased 
length of line. The engineer having less command of the ground, 
owing to the reduced area he has to deal with and the greater abrupt¬ 
ness of the slopes, is liable to be frustrated in his attempt to get his 
line carried in the desired direction. 





22 


HIGHWAY CONSTRUCTION 


It is a common practice to run a mountain survey up hill, but 
this should be avoided. Whenever an acute-angled zigzag is met 
with on a mountain road near the summit, the inference to be drawn 
is that the line being carried up hill on reaching the summit was 
too low and the zigzag was necessary to reach the desired pass. The 
only remedy in such a case is by a resurvey beginning at the summit 
and running down hill. This method requires a reversal of that 
usually adopted. The grade line is first staked out and its horizontal 
location surveyed afterwards. The most appropriate instrument for 
this work is a transit with a vertical circle on which the telescope may 
be set to the angle of the maximum grade. 

Loss of Height. Loss of height is to be carefully avoided in a 
mountain road. By loss of height is meant an intermediate rise in a 
descending grade. If a descending grade is interrupted by the intro¬ 
duction of an unnecessary ascent, the length of the road will be in¬ 
creased over that due to the continuous grade by the length of the 
portion of the road intervening between the summit of the rise and 
the point in the road on a level with that rise—a length which is double 
that due on the gradient to the height of the rise. For example, 
if a road descending a mountain rises at some intermediate point to 
cross over a ridge or spur, and the height ascended amounts to 110 
feet before the descent is continued, such a road would be just one 
mile longer than if the descent had been uninterrupted; for 110 feet 
is the rise due to a half-mile length at 1: 24. 

Water on Mountain Roads. Water is needed by the work¬ 
men and during the construction of the road; it is also very necessary 
for the traffic, especially during hot weather; and if the road exceeds 
5 miles in length, provision should be made to have it either close 
to or within easy reach of the road. With a little ingenuity the 
water from springs above the road, if such exist, can be led down to 
drinking fountains for men, and to troughs for animals. 

In a tropical country it would be a matter for serious consider¬ 
ation if the best line for a mountain road 10 miles in length or up¬ 
wards, but without water, should not be abandoned in favor of a 
worse line with a water supply available. 

Halting Places. On long lines of mountain roads halting 
places should be provided at frequent intervals. 




HIGHWAY CONSTRUCTION 


23 


Alignment. No rule can be laid down for the alignment of a 
road; it will depend both upon the character of the traffic on it and 
upon the ‘‘lay of the land.” To promote economy of transportation 
it should be straight; but if straightness is obtained at the expense 
of easy grades that might have been obtained by deflections and 
increase in length, it will prove very expensive to the community 
that uses it. 

Where curves are necessary, employ the greatest radius possible 
and never less than fifty feet. They may be circular or parabolic. 
The parabolic will be found exceedingly useful for joining tangents 
of unequal length, and for following contour lines; its curvature 
being least at its beginning and ending, makes the deviations from 
a straight line less strongly marked than by a circular arc. 

When a curve occurs on an ascent, the grade at that place must 
be diminished in order to compensate for the additional resistance of 
the curve. 

The width of the wheel way on curves must be increased. This 
increase should be one-quarter of the width for central angles between 
90 and 120 degrees, and one-half for angles between 60 and 90 degrees. 
Excessive crookedness of alignment is to be avoided, for any unneces¬ 
sary length causes a constant threefold waste; first, of the interest 
of the capital expended in making that unnecessary portion; secondly, 
of the ever recurring expense of repairing it; and thirdly, of the time 
and labor employed on travelling over it. 

The curving road around a hill may be often no longer than the 
straight one over it, for the latter is straight only with reference to 
the horizontal plane, while it is curved as to the vertical plane; the 
former is curved as to the horizontal plane, but straight as to the 
vertical plane. Both lines curve, and we call the one passing over 
the hill straight only because its vertical curvature is less apparent 
to our eyes. 

The difference in length between a straight road and one which 
is slightlv curved is very small. If a road between two places ten 
miles apart were made to curve so that the eye could nowhere see 
farther than one-quarter of a mile of it at once, its length would 
exceed that of a straight road between the same points by only about 
four hundred and fifty feet. 



24 


HIGHWAY CONSTRUCTION 


Zigzags. The method of surmounting a height by a series of 
zigzags or by a series of reaches with practicable curves at the turns, 
is objectionable. 

(1) An acute-angled zigzag obliges the traffic to reverse its 
direction without affording it convenient room for the purpose. The 
consequence is that with slow traffic a single train of vehicles is 
brought to a stand, while if two trains of vehicles travelling in opposite 
directions meet at the zigzag a block ensues. 

(2) With zigzags little progress is made towards the ultimate 
destination of the road; height is surmounted, but horizontal distance 
is increased for which there is no necessity or compensation. 

(3) Zigzags are dangerous. In case of a runaway down hill 
the zigzag must prove fatal. 

(4) If the drainage cannot be carried clear of the road at the 
end of each reach, it must be carried under the road in one reach only 
to appear again at the next, when a second bridge, culvert, or drain 
will be required, and so on at the other reaches. If the drainage can 
be carried clear at the termination of each reach, the lengths-between 
the curves will be very short, entailing numerous zigzag curves, which 
are expensive to construct and maintain. 

* Final Location. The route being finally determined upon, it 
requires to be located. This consists in tracing the line, placing a 
stake at every 100 feet on the straight portions and at every 50 or 
25 feet on the curves. At the tangent point of curves, and at points 
of compound and reverse curves, a larger and more permanent stake 
should be placed. Lest those stakes should be disturbed in the 
process of construction, their exact distance from several points 
outside of the ground to be occupied by the road should be carefully 
measured and recorded in the notebook, so that they may be replaced. 
The stakes above referred to show the position of the center line of 
the road, and form the base line from which all operations of con¬ 
struction are carried on. Levels are taken at each stake, and cross 
levels are taken at every change of longitudinal slope. 

Construction Profile. The construction or working profile 
is made from the levels obtained on location. It should be drawn to a 
horizontal scale of 400 feet to the inch and a vertical scale of 20 feet’/ 1 
to the inch. Fig. 7 represents a portion of such a profile. The’ • 




HIGHWAY CONSTRUCTION 


25 


figures in column A represent the elevation of the ground at every 
100 feet, or where a stake has been driven, above datum. The 
figures in column B are the elevations of the grade above datum. 
The figures in column C indicate the depth of cutting or height of 
fill; they are obtained by taking the difference between the level of 
the road and the level of the surface of the ground. The straight line 

oo 


.Oi 

CAZ 



at the top represents the grade of the road; the upper surface of the 
road when finished would be somewhat higher than this, while the 
given line represents what is termed the sub-grade or formation level. 
All the dimensions refer to the formation level, to which the surface 
of the ground is to be formed to receive the road covering. 

At all changes in the rate of inclination of the grade line a heavier 
vertical line should be drawn. * 

Gradient. The grade of a line is its longitudinal slope, and 
is designated by the proportion between its length and the difference 
of height of its two extremes. The ratio of these two qualities gives 
it its name; if the road ascends or falls one foot in every twenty feet 
of its length, it is said to have a grade of 1: 20 or a 5 per cent grade. 
Grades are of two kinds, maximum and minimum. The maximum 
is the steepest which is to be permitted and which on no account is to be 
exceeded. The minimum is the least allowable for good drainage. 
(For method of designating grades see Table 9). 

Determination of Gradients. The maximum grade is fixed 
by two considerations, one relating to the power expended in ascend¬ 
ing, the other to the acceleration in descending the incline. 

There is a certain inclination, depending upon the degree of 
perfection given to the surface of the road, which cannot be exceeded 

















26 


HIGHWAY CONSTRUCTION 


without a direct loss of tractive power. This inclination is that in 
descending which, at a uniform speed, the traces slacken, or which 
causes the vehicles to press on the horses; the limiting inclination 
within which this effect does not take place is the angle of repose. 

TABLE 9. 


American method. 
Feet per 100 feet. 

English method. 

Feet per mile. 

Angle with the horizon. 

1 

4 

1 

400 

13.2 

0° 

8' 

36" 

1 

2 

1 

200 

26.4 

0 

17 

11 

4 

1 

150 

39.6 

0 

22 

55 

1 

1 

100 

52.8 

0 

34 

23 

H 

1 

80 • 

66 

.0 

42 

58 

\\ 

1 

66§ 

79.2 

0 

51 

28 

if 

1 

571 

92.A 

1 

0 

51 

2 

1 

50 

105.6 

1 

8 

6 

21 

1 

44i 

118.8 

1 

17 ' 

39 

2i 

1 

40 

132 

1 

25 

57 

2f 

1 

364 

145.2 

1 

34 

22 

3 

1 

334 

158.4 

1 

43 

08 

31 

1 

30 f 

171 .6 

1 

51 

42 

34 

1 

284 

184.8 

2 

0 

16 

3f 

1 

26§ 

198 

2 

8 

51 

4 

1 

25 

211.2 

1 

17 

26 

H 

1 

234 

224.4 

2 

26 

10 

44 

1 

224 

237.6 

2 

34 

36 

4f 

1 

21 

250.8 

2 

43 

35 

5 

1 

20 

264 

2 

51 

44 

6 

1 

134 

316.8 

3 

26 

12 

7 

1 

14f 

369.6 

4 

0 

15 

8 

1 

124 

422.4 

4 

34 

26 

9 

1 

1H 

475.2 

5 

8 

31 

10 

1 

10 

528 

5 

42 

37 


The angle of repose for any given road surface can be easily 
ascertained from the tractive force required upon a level with the 
same character of surface. Thus if the force necessary on a level 
to overcome the resistance of the load is ^ of its weight, then the 
same fraction expresses the angle of repose for that surface. 

On all inclines less steep than the angle of repose a certain 
amount of tractive force is necessary in the descent as well as in 
the ascent, and the mean of the two drawing forces, ascending and 
descending, is equal to the force along the level of the road. Thus 
on such inclines, as much mechanical force is gained in the descent 
as is lost in the ascent. From this it might be inferred that when a 
vehicle passes alternately each way along the road, no real loss is 




















HIGHWAY CONSTRUCTION 


27 


occasioned by the inclination of the road; such is not, however, 
practically the fact with animal power, for while it is necessary in 
the ascending journey to have either a less or a greater number of 
horses than would be requisite if the road were entirely level, no 
corresponding reduction can be made in the descending journey. 
On inclines which are more steep than the angle of repose, the load 
presses on the horses during their descent, so as to impede their 
action, and their power is expended in checking the descent of the 
load; or if this effect be prevented by the use of any form of drag or 
brake, then the power expended on such a drag or brake corresponds 
to an equal quantity of mechanical power expended in the ascent, 
for which no equivalent is obtained in the descent. 

The maximum grade for a given road will depend (1) upon the 
class of traffic that will use it, whether fast and light, slow and heavy, 
or mixed, consisting of both light and heavy; (2) upon the character 
of the pavement adopted; and (3) upon the question of cost of con¬ 
struction. Economy of motive power and low cost of construction are 
antagonistic to each other,,and the engineer will have to weigh the 
two in the balance. 

For fast and light traffic the grades should not exceed 2 per 
cent; for mixed traffic 3 per cent may be adopted; while for slow 
traffic combined with economy 5 per cent should not be exceeded. 
This grade is practicable but not convenient. 

Minimum Grade. From the previous considerations it would 
appear that an absolutely level road was the one to be sought for, but 
this is not so; there is a minimum or least allowable grade which the 
road must not fall short of, as well as a maximum one which it must 
not exceed. If the road was perfectly level in its longitudinal direc¬ 
tion, its surface could not be kept free from water without giving it 
so great a rise in its middle as would expose vehicles to the danger of 
overturning. The minimum grade commonly used is 1 per cent. 

Undulating Grades, From the fact that the power required 
to move a load at a given velocity on a level road is decreased on a 
descending grade to the same extent it is increased in ascending the 
same grade, it must not be inferred that the animal force expended 
in passing alternately each way over a rising and falling road will 
train as much in descending the several inclines as it will lose in ascend- 

O 


28 


HIGHWAY CONSTRUCTION 


ing them. Such is not the case. The animal force must be sufficient, 
either in power or number, to draw the load over the level portions 
and up the steepest inclines of the road, and in practice no reduction 
in the number of horses can be made to correspond with the decreased 
power required in descending the inclines. 

The popular theory that a gentle undulating road is less fatiguing 
to horses than one which is perfectly level is erroneous. The asser¬ 
tion that the alternations of ascent, descent, and levels call into play 
different muscles, allowing some to rest while others are exerted, 
and thus relieving each in turn, is demonstrably false, and con¬ 
tradicted by the anatomical structure of the horse. Since this doc¬ 
trine is a mere popular error, it should be utterly rejected, not only 
because false in itself, but still more because it encourages the building 
of undulating roads, and this increases the labor and cost of trans¬ 
portation upon them. 

Level Stretches. On long ascents it is generally recom¬ 
mended to introduce level or nearly level stretches at frequent inter¬ 
vals in order to rest the animals. These are objectionable when 
they cause loss of height, and animals will be more rested by halting 
and unharnessing for half an hour than by travelling over a level 
portion. The only case which justifies the introduction of levels 
into an ascending road is where such levels will advance the road 
towards its objective point; where this is the case there will be no 
loss of either length or height, and it will simply be exchanging a 
level road below for a level road above. 

Establishing the Grade. When the profile of a proposed 
route has been made, a grade line is drawn upon it (usually in red) in 
such a manner as to follow its general slope, but to average its irregular 
elevation and depressions. 

If the ratio between the whole distance and the height of the line 
is less than the maximum grade intended to be used, this line will be 
satisfactory; but if it be found steeper, the cuttings or the length 
of the line will have to be increased; the latter is generally preferable. 

The apex or meeting point of all curves should be rounded off' 
by a vertical curve, as shown in Fig. 8, thus slightly changing the 
grade at and near the point of intersection. A vertical curve rarely 
need extend more than 200 feet each way from that point. 



HIGHWAY CONSTRUCTION 


29 


Let A B, B C, be two grades in profile, intersecting at station B, 
and let A and C be the adjacent stations. It is required to join the 

B 



grades by a vertical curve extending from A to C. Imagine a chord 
drawn from A to C. The elevation of the middle point of the chord 
will be a mean of the elevations of the grade at A and C, and one- 
half of the difference between this and the elevation of the grade at 
B will be the middle ordinate of the curve. Hence we have 


M = 




grade A + grade C 


— grade B 


). 


in which M equals the correction in grade for the point B. The 
correction for any other point is proportional to the square of its 
distance from A or C. Thus the correction A + 25 is M; at 
A + 50 it is J M; at A -f 75 it is T 9 g M; and the same for corre¬ 
sponding points on the other side of B. The corrections in this case 
shown are subtractive, since M is negative. They are additive 
when M is positive, and the curve concave upward. 

WIDTH AND TRANSVERSE CONTOUR. 


A road should be wide enough to accommodate the traffic for 
which it is intended, and should comprise a wheel way for vehicles 
and a space on each side for pedestrians. 

The wheelway of country highways need be no wider than is 
absolutely necessary to accommodate the traffic using it; in many 
places a track wide enough for a single team is all that is necessary. 
But the breadth of the land appropriated for highway purposes 
should be sufficient to provide for all future increase of traffic. The 
wheelwavs of roads in rural sections should be double; that is, one 

t/ 

portion paved (preferably the center), and the ether left with the 














30 


HIGHWAY CONSTRUCTION 


natural soil. The latter if kept in repair will for at least one-half 
the year be preferred by teamsters. 

The minimum width of the paved portion, if intended to carry 
two lines of travel, is fixed by the width required to allow two vehicles 
to pass each other safely. This width is 16 feet. If intended for 
a single line of travel, 8 feet is sufficient, but suitable turnouts must be 
provided at frequent intervals. The most economical width for any 
roadway is some multiple of eight. 

Wide roads are the best; they expose a larger surface to the 
drying action of the sun and wind, and require less supervision than 
narrow ones. Their first cost is greater than narrow ones, and that 
nearly in the ratio of the increased width. 

The cost of maintaining a mile of road depends more upon the 
extent of the traffic than upon the extent of its surface, and unless 
extremes be taken, the same quantity of material will be necessary 
for the repair of the road whether wide or narrow, which is subjected 
to the same amount of traffic. The cost of spreading the materials 
over the wide road will be somewhat greater, but the cost of the 
materials will be the same. On narrow roads the traffic, being 
confined to one track, will wear more severely than if spread over a 
wider surface. 

The width of land appropriated for road purposes varies in the 
United States from 494 feet to 66 feet; in England and France from 
26 to 66 feet. And the width or space macadamized is also subject 
to variation; in the United States the average width is 16 feet; in 
France it varies between 16 and 22 feet; in Belgium 8} feet seems 
to be the regular width, while in Austria from 144 to 26J feet. 

Transverse Contour. The center of all roadways should 
be higher than the sides. The object of this is to facilitate the flow 
of the rain water to the gutters. Where a good surface is maintained 
a very moderate amount of rise is sufficient for this purpose. Earth 
roads require the most and asphalt the least. The rise should bear 
a certain proportion to the width of the carriageway. The most 
suitable proportions for the different paving materials is shown in 
table 10. 

Form of Transverse Contour. All authorities agree that 
the form should be convex, but they differ in the amount and form 







HIGHWAY CONSTRUCTION 


31 


of the convexity. Circular arcs, two straight lines joined by a circular 
arc, and ellipses, all have their advocates. 

TABLE 10. 

Kind of Surface. Proportions of the 

Carriageway. Width. 

Earth Rise at center ^ 

Gravel “ “ “ gV- 

Broken Stone “ “ “ ^ 

For country roads a curve of suitable convexity may be obtained 
as follows: Give J of the total rise at \ the width from the center 
to the side, and f of the total rise at \ the width (Fig. 9). 

Excessive height and convexity of cross-section contract the 
width of the wheelway, by concentrating the traffic at the center, 
that being the only part where a vehicle can run upright. The force 
required to haul vehicles over such cross-sections is increased, be- 


to 

< 


<D 

< 







Fig. 9. 

cause an undue proportion of the load is thrown upon two wheels 
instead of being distributed equally over the four. The continual 
tread of horses’ feet in one track soon forms a depression which holds 
water, and the surface is not so dry as with a flat section, which allows 

7 %j ' 

the traffic to distribute itself over the whole width. 

Sides formed of straight lines are also objectionable. They 
wear hollow, retain water, and defeat the object sought by raising 
the center. 

The required convexity should be obtained by rounding the 
formation surface, and not by diminishing the thickness of the 
covering at the sides. 

Although on hillside and mountain roads it is generally recom- 

mended that the surface should consist of a single slope inclining 

inwards, there is no reason for or advantage gained by this method. 

The form best adapted to these roads is the same as for a road under 

ordinary conditions. 

•/ 

With a roadway raised in the center and the rain water draining 
off to gutters on each side, the drainage will be more effectual and 








32 


HIGHWAY CONSTRUCTION 


speedy than if the drainage of the outer half of the road has to pass 
over the inner half. The inner half of such a road is usually sub¬ 
jected to more traffic than the outer half. If formed of a straight 
incline, this side will be worn hollow and retain water. The inclined 
flat section never can be properly repaired to withstand the traffic. 
Consequently it never can be kept in good order, no matter how 
constantly it may be mended. It is always below par and when 
heavy rain falls it is seriously damaged. 

DRAINAGE. 

In the construction of roads, drainage is of the first importance. 
The ability of earth to sustain a load depends in a large measure upon 
the amount of moisture retained by it. Most earths form a good 
firm foundation so long as they are kept dry, but when wet they lose 
their sustaining power, becoming soft and incoherent. 

The drainage of roadways is of two kinds, viz., surface and sub¬ 
surface. The first provides for the speedy removal of all water 
falling on the surface of the road; the second provides for the removal 
of the underground water found in the body of the road, a thorough 
removal of which is of the utmost importance and essential to the 
life of the road. A road covering placed on a wet undrained bottom 
will be destroyed by both water and frost, and will always be trouble¬ 
some and expensive to maintain; perfect subsoil drainage is a neces¬ 
sity and will be found economical in the end even if in securing it 
considerable expense is required. 

The methods employed for securing the subsoil drainage must , 
be varied according to the character of the natural soil, each kind of 
soil requiring different treatment. 

The natural soil may be divided into the following classes: 
silicious, argillaceous, and calcareous; rock, swamps, and morasses. 

The silicious and calcareous soils, the sandy loams and rock, 
present no great difficulty in securing a dry and solid foundation. 
Ordinarily they are not retentive of water and therefore require no 
underdrains; ditches on each side of the road will generally be found 
„ sufficient. 

The argillaceous soils and softer marls require more care; they 
retain water and are difficult to compact, except at the surface; 
and they are very unstable under the action of water and frost. 





HIGHWAY CONSTRUCTION 


33 


i lie drainage of these soils may he effected by transverse drains 
and deep side ditches of ample width. The transverse drains are 
placed across the road, not at right angles but in the form of an 
inverted V with the point directed up hill; the depth at the angle 
point should not be less than 18 inches below the subgrade surface, 
and each branch should descend from the apex to the side ditches 
with a fall of not less than 1 inch in 5 feet. The distance apart of 
these drains will depend upon the wetness of the soil; in the case of 
very wet soil they should be at intervals of 15 feet, which may be 
increased to 25 feet as the ground becomes drier and firmer. 

The transverse drains are best formed of unglazed circular tile 
of a diameter not less than 3 inches, jointed with loose collars. The 
tiles are made from terra cotta or burnt clay, are porous, and are 
superior to all other kinds of drains. They carry off the water with 
greater ease, rarely if ever get choked up, and only require a slight 
inclination to keen water moving through them. 



Fig. 11. Silt Basin. 


The tiles are made in a variety of forms, as horseshoe, sole, 
double sole, and round, the name being derived from the shape of 
the cross-sections. Round tile is superior to all other forms. The 
inside diameter of these tiles varies from \\ to fi inches, but they are 
manufactured as large as 24 inches. Pieces of the larger pipe serve 
as collars for the smaller ones. They are made in lengths of 12, 
14 and 24 inches, and in thickness of shell from } of an inch to 1 inch. 

The collar which encircles the joint of the small tile allows a 
large opening, and at the same time prevents sand and silt from 

































34 


HIGHWAY CONSTRUCTION 


entering the drain. Perishable material should not be used for 

o 

jointing. When laid in the ditch they should be held in place by 
small stones. Connections should be made by proper A-branches. 

The outlets may be formed by building a dwarf wall of brick or 
stone, whichever is the cheapest or most convenient in the locality. 
The outlet should be covered with an iron grating to prevent vermin 
entering the drain pipes, building nests and thus choking up the 
waterway. (See Fig. 12.) 



Silt-basins should be constructed at all junctions and wherever 
else they may be considered necessary; they, may be made from a 
single 6-inch pipe (Fig. 11) or constructed of brick masonry. 

The trenches for the tile should be excavated at least 3 feet 

4 * 

wide on top and 12 inches on the bottom. After the tiles are laid 
the trenches must be filled to subgrade level with round field or 


cobble stones; stones with angular edges are unsuitable for this 
purpose. Fine gravel, sand, or soil should not be placed over the 
drains. Bricks and flat stones may be substituted for the tiles, 
and the trenches filled as above stated. 

As tile drains are more liable to injury from frost than those 
of either brick or stone, their ends at the side ditches should not 
in very cold climates be exposed directly to the weather, but may 
terminate in blind drains, or a few lengths of vitrified clay pipe 
reaching under the road a distance of about 3 to 4 feet from the 
inner slope of the ditch. 

Another method of draining the roadbed offering security from 
frost is by one or more rows of longitudinal drains. These drains 
are placed at equal distances from the side ditches and from each 
other, and discharge into cross drains placed from 250 to 300 feet 




































HIGHWAY CONSTRUCTION 


35 


apart, more or less, depending on the contour of the ground. The 
cross drains into which they discharge should be of ample dimensions. 
On these longitudinal lines' of tiles the introduction of catch basins 
at intervals of 50 feet will facilitate the removal of the water. These 
catch basins may be excavated three or more feet square and as deep 
as the tiles are laid. After the tiles are laid the pit is filled with gravel 
and small stones. 



Fall of Drains. It is a mistake to give too much fall to small 
drains, the only effect of which is to produce such a current through 
them as will wash away or undermine the ground around them, and 
ultimately cause their own destruction. When a drain is once closed 
by any obstruction no amount of fall which could be given it will 



again clear the passage. A drain with a considerable current through 
it is much more likely to be stopped from foreign matter carried into 
it, which a less rapid stream could not have transported. 

A fall of 1 inch in 5 feet will generally be sufficient, and 1 inch 
in 30 inches should never be exceeded. 



Side Ditches are provided to carry away the subsoil water 
from the base of the road, and the rain water which falls upon its 
surface; to do this speedily they must have capacity and inclination 
















36 


HIGHWAY CONSTRUCTION 


proportionate to the amount of water reaching them. The width 
of the bed should not be less than 18 inches; the depth will vary with 
circumstances, but should be such that the water surface shall not 
reach the subgrade, but remain at least 12 inches below the crown 
of the road. The sides should slope at least 1J to 1. 

The longitudinal inclination of the ditch follows the configura¬ 
tion of the general topography, that is, the lines of natural drainage. 
When the latter has to be aided artificially, grades from 1 in 500 to 
1 in 800 will usually answer. 



In absorbent soil less fall is sufficient, and in certain cases level 
ditches are permissible. The slopes of the ditches must be protected 
where the grade is considerable. This can be accomplished by sod 
revetments, riprapping, or paving. 

These ditches may be placed either on the road or land side of the 
fence. In localities where open ditches are undesirable they may be 
constructed as shown in Figs. 13 to 17, and may be formed of stone 



or tile pipe, according to the availability of either material. If for 
any reason two can not be built, build one. 

Springs found in the roadbed should be tapped and led into the 
side ditches. 

Drainage of the Surface. The drainage of the roadway 
surface depends upon the preservation of the cross-section, with 
regular and uninterrupted fall to the sides, without hollows or ruts 
in which the water can lie, and also upon the longitudinal fall of the 
















HIGHWAY CONSTRUCTION 


.‘37 


road. If this is not sufficient the road becomes flooded during heavy 
rainstorms and melting snow, and is considerably damaged. 

I he removal of surface water from country roads may be effected 
by the side ditches, into which, when there are no sidewalks, the 
water flows directly. When there are sidewalks, gutters are formed 
between the roadway and footpath, as shown in Figs. 13 to 17, and 
the water is conducted from these gutters into the side ditches by 
tile pipes laid under the walks at intervals of about 50 feet. The 
entrance to these pipes should be protected against washing by a 
rough stone paving. In the case of covered ditches under the footpath 
the water must be led into them by first passing through a catch 
basin. These are small masonry vaults covered with iron gratings to 
prevent 'the ingress of stones, leaves, etc. Connection from the 
catch basin is made by a tile pipe about 6 inches in diameter. The 
mouth of this pipe is placed a few feet above the bottom of the catch 
basin, and the space below it acts as a depository for the silt carried 
by the water, and is cleaned out periodically. The catch basins may 
be placed from 200 to 300 feet apart. They should be made of 
dimensions sufficient to convey the amount of water which is liable 
to flow into them during heavy and continuous rains. 

If on inclines the velocity of the water is greater than the nature 
of the soil will withstand, the gutters will be roughly paved. In all 
cases, the slope adjoining the footpath should be covered with sod. 

A velocity of 30 feet a minute will not disturb clay with sand and 
stone. 40 feet per minute will move coarse sand. 60 feet a minute 
will move gravel. 120 feet a minute should move round pebbles 1 inch 
in diameter, and 180 feet a minute will move angular stones If inches 
in diameter. 

The scour in the gutters on inclines may be prevented by small 
weirs of stones or fascines constructed by the roadmen at a nominal 
cost. At junctions and crossroads the gutters and side ditches re¬ 
quire careful arrangement so that the water from one road may not 
be thrown upon another; cross drains and culverts will be required 
at such places. 

Water Breaks to turn the surface drainage into the side ditches 
should not be constructed on improved roads. They increase the 
grade and are an impediment to convenient and easy travel. Where 




38 


HIGHWAY CONSTRUCTION 


it is necessary that water should cross the road a culvert should be 

V 

built. 

On the side hill or mountain roads catch-water ditches should 
be cut on the mountain side above the road, to cut off and convey the 
drainage of the ground above them to the neighboring ravines. The 
size of these ditches will be determined by the amount of rainfall, 
extent of drainage from the mountain which they intercept, and by the 
distances of the ravine water courses on each side. 

The inner road gutter should be of ample dimensions to carry 
off the water reaching it; when in soil, it should be roughly paved with 
stone. When paving is not absolutely necessary, but it is desirable 
to arrest the scouring action of running water during heavy rains, 
stone weirs may be erected across the gutter at convenient intervals. 
The outer gutter need not be more than 12 inches wide and 9 inches 
deep. The gutter is formed by a depression in the surface of the 
road close to the parapet or revetted earthen protection mound. The 
drainage which falls into this gutter is led off through the parapet, 
or other roadside protection at frequent intervals. The guard stones 
on the outside of the road are placed in and across this gutter, just 
below the drainage holes, so as to turn the current of the drainage 
into these holes or channels. On straight reaches, with parapet 
protection, drainage holes with guard stones should be placed every 
20 feet apart. Where earthen mounds are used and it may not be 
convenient to have the drainage holes or channels every 20 feet, the 
guardstones are to be placed in advance of the gutter to allow the 
drainage to pass behind them. This drainage is either to be run off 
at the cross drainage of the road, or to be turned off as before by a 
guard stone set across the gutter. 

At re-entering turns, where the outer side of the road requires 
particular protection, guard stones should be placed every 4 feet. 
As all re-entering turns should be protected by parapets, the drainage 
holes through them may be placed as close together as desired. 

Culverts are necessary for carrying under a road the streams 
it crosses, and also for conveying the surface water collected in the 
side ditches from the upper side to that side on which the natural 
water courses lie. 

Especial care is required to provide an ample way for the water 





HIGHWAY CONSTRUCTION 


39 


to be passed. It the culvert is too small, it is liable to cause a washout, 
entailing interruption of traffic and cost of repairs, and possibly may 
cause accidents that will recpiire payment of large sums for damages. 


On the other hand, if the culvert is made unnecessarily large, the 
cost of construction is needlessly increased. 

The area of waterway required depends (1) upon the rate of 
rainfall; (2) the kind and condition of the soil; (3) the character 


and inclination of the surface; (4) the condition and inclination of 
the bed of the stream; (5) the shape of the area to be drained, and 
the position of the branches of the stream; (6) the form of the mouth 
and the inclination of the bed of the culvert; and (7) whether it is 
permissible to back the water up above the culvert, thereby causing 
it to discharge under a head. 

(1) It is the maximum rate of rainfall during the severest storms 
which is required in this connection. This varies greatly in different 
sections of the country. 

The maximum rainfall as shown by statistics is about one inch 
per hour (except during heavy storms), equal to 3,630 cubic feet per 
acre. Owing to various causes, not more than 50 to 75 per cent of 
this amount will reach the culvert within the same hour. 

Inches of rainfall X 3,630 = cubic feet per acre. 

Inches of rainfall X 2,323,200 = cubic feet per square mile. 

(2) The amount of water to be drained off will depend upon the 
permeability of the surface of the ground, which will vary greatly 
with the kind of soil, the degree of saturation, the condition of the 
cultivation, the amount of vegetation, etc. 

(3) The rapidity with which the water will reach the water 
course depends upon whether the surface is rough or smooth, steep 
or flat, barren or covered with vegetation, etc. 

(4) The rapidity with which the water will reach the culvert 
depends upon whether there is a well-defined and unobstructed 
channel, or whether the water finds its way in a broad thin sheet. 
It the water course is unobstructed and has a considerable inclination, 
the water may arrive at the culvert nearly as rapidly as it falls; but 
if the channel is obstructed, the water may be much longer in passing 
the culvert than in falling. 

(5) The area of waterway depends upon the amount of the area 






40 


HIGHWAY CONSTRUCTION 


to be drained; but in many cases the shape of this area and the posi¬ 
tion of the branches of the stream are of more importance than the 
amount of the territory. For example, if the area is long and narrow, 
the water from the lower portion may pass through the culvert before 
that from the upper end arrives; or, on the other hand, if the upper 
end of the area is steeper than the lower, the water from the former 
may arrive simultaneously with that from the latter. Again, if the 
lower part of the area is better supplied with branches than the upper 
portion, the water from the former will be carried past the culvert 
before the arrival of that from the latter; or, on the other hand, if 
the upper part is better supplied with branch water courses than 
the lower, the water from the whole area may arrive at the culvert 
at nearly the same time. In large areas the shape of the area and 
the position of the water courses are very important considerations. 

(6) The efficiency of a culvert may be very materially increased 
by so arranging the upper end that the water may enter into it without 
being retarded. The discharging capacity of a culvert can be greatly 
increased by increasing the inclination of its bed, provided the channel 
below will allow the water to flow away freely after having passed 
the culvert. 

(7) The discharging capacity of a culvert can be greatly increased 
by allowing the water to dam up above it. A culvert will discharge 
twice as much under a head of four feet as under a head of one foot. 
This can be done safely only with a well constructed culvert. 

The determination of the values of the different factors entering 
into the problem is almost wholly a matter of judgment. An estimate 
for any one of the above factors is liable to be in error from 100 to 
200 per cent, or even more, and of course any* result deduced from 
such data must be very uncertain. Fortunately, mathematical exact¬ 
ness is not required by the problem nor warranted by the data. The 
question is not one of 10 or 20 per cent of increase; for if a 2-foot pipe 
is sufficient, a 3-foot pipe will probably be the next size, an increase 
of 225 per cent; and if a 6-foot arch culvert is too small, an 8-foot will 
be used, an increase of 180 per cent. The real question is whether 
a 2-foot pipe or an 8-foot arch culvert is needed. 

Valuable data on the proper size of any particular culvert may 
be obtained (1) by observing the existing openings on the same 






highway construction 


41 


stream; (2) by measuring, preferably at time of high water, a cross- 
section of the stream at some narrow place; and (3) determining the 
height of high water as indicated by drift and the evidence of the 
inhabitants of the neighborhood. 

On mountain roads or roads subjected to heavy rainfall culverts 
of ample dimensions should be provided wherever required, and it 
will be more economical to construct them of masonry. In localities 
where boulders and other debris are likely to be washed down during 
wet weather, it will be a good precaution to construct catch pools at 
the entrance of all culverts and cross drains for the reception of 
such matter. In hard soil or rock these catch pools will be simple 
well-like excavations, with their bottom two or three feet below the 
entrance sill or floor of the culvert or drain. Where the soil is soft 
they should be lined with stone laid dry; if very soft, with masonry. 
The size of the catch pools will depend upon the width of the drainage 
works. They should be wide enough to prevent the drains from 
being injured by falling rocks and stones of a not inordinate size. 

The use of catch pools obviates the necessity of building culverts 
and drains at an angle to the axis of the road. Oblique structures 
are objectionable, as being longer than if set at right angles and by 
reason of the acute- and obtuse-angled terminations to their piers, 
abutments, and coverings. 

Materials for Culverts. Culverts may be of stone, brick, vitri¬ 
fied earthenware, or iron pipe. Wood should be absolutely avoided. 

For small streams and a limited surface of rainfall either class 
of pipes, in sizes varying from 12 to 24 inches in diameter, will serve 
excellently. They are easily laid, and if properly bedded, with the 
earth tamped about them, are very permanent. Their upper surface 
should be at least IS inches below the road surface, and the upper 
end should be protected with stone paving so arranged that the water 
can in no case work in around the pipe. 

When the flow of water is estimated to be too great for two lines 
of 24-inch pipes, a culvert is required. If stone abounds, it may be 
built of large roughly squared stones laid either dry or in mortar. 
When the span required is more than 5 feet, arch culverts either of 
stone or brick masonry may be employed. For spans above 15 feet 
the structure required becomes a bridge. 



42 


HIGHWAY CONSTRUCTION 


Earthenware Pipe Culverts. Construction. In laying the 
pipe the bottom of the trench should be rounded out.to fit the lower 
half of the body of the pipe with proper depressions for the sockets. 
If the ground is soft or sandy, the earth should be rammed carefully, 
but solidly in and around the lower part of the pipe. The top surface 
of the pipe should, as a rule, never be less than 18 inches below the 
surface of the roadway, but there are many cases where pipes have 
stood for several years under heavy loads with only 8 to 12 inches of 
earth over them. No danger from frost need be apprehended, pro¬ 
vided the culverts are so constructed that the water is carried away 
from the level end. Ordinary soft drain tiles are not in the least 
affected by the expansion of frost in the earth around them. 

The freezing of water in the pipe, particularly if more than half 
full, is liable to burst it; consequently the pipe should have a suffi¬ 
cient fall to drain itself, and the outside should be so low that there 
is no danger of back waters reaching the pipe. If properly drained, 
there is no danger from frost. 

Jointing. In many cases, perhaps in most, the joints are 
not calked. If this is not done, there is liability of the water being 
forced out of the joints and washing away the soil from around the 
pipe. Even if the danger is not very imminent, the joints of the 
larger pipes, at least, should be calked with hydraulic cement, since 
the cost is very small compared with the insurance against damage 



thereby secured. Sometimes the joints are calked with clay. Every 
culvert should be built so that it can discharge water under a head 
without damage to itself. 












































































HIGHWAY CONSTRUCTION 


43 


Although often omitted, the end sections should be protected 
with a masonry or timber bulkhead. The foundation of the bulk¬ 
head should be deep enough not to be disturbed by frost. In con¬ 
structing the end wall, it is well to increase the fall near the outlet 
to allow for a possible settlement of the interior sections. When 
stone and brick abutments are too expensive, a fair substitute can 
be made by setting posts in the ground and spiking plank to them. 
When planks are used, it is best to set them with considerable inclina¬ 
tion towards the roadbed to prevent their being crowded outward 
by the pressure of the embankment. The upper end of the culvert 
should be so protected that the water will not readily find its way 



along the outside of the pipes, in case the mouth of the culvert should 
become submerged. 

When the capacity of one pipe is not sufficient, two or more 
may be laid side by side as shown in Fig. 19. Although the two 
small pipes do not have as much discharging capacity as a single 
large one of equal cross-section, yet there is an advantage in laying 
two small ones side by side, since the water need not rise so high 
to utilize the full capacity of the two pipes as would be necessary 
to discharge itseif through a single one of large size. 

Iron Pipe Culverts. During recent years iron pipe has been 
used for culverts on many prominent railroads, and may be used on 
roads in sections where other materials are unavailable. 

In constructing a culvert with cast-iron pipe the points requiring 



















44 


.HIGHWAY CONSTRUCTION 


particular attention are (1) tamping the soil tightly around the pipe 
to prevent the water from forming a channel along the outside, and 
(2) protecting the ends by suitable head walls and, when necessary, 
laying riprap at the lower end. The amount of masonry required 
for the end walls depends upon the relative width of the embankment 
and the number of sections of pipe used. For example, if the em¬ 
bankment is, say, 40 feet wide at the base, the culvert may consist of 
three 12-foot lengths of pipe and a light end wall near the toe of 
the bank; but if the embankment is, say, 32 feet wide, the culvert 
may consist of two 12-foot lengths of pipe and a comparatively heavy 
end wall well back from the toe of the bank. The smaller sizes of 
pipe usually come in 12-foot lengths, but sometimes a few G-foot 



lengths are included for use in adjusting the length of the culvert 
to the width of the bank. The larger sizes are generally 6 feet long. 

EARTHWORK. 


The term “earthwork” is applied to all the operations per¬ 
formed in the making of excavation and embankments. In its 
widest sense it comprehends work in rock as well as in the looser 
materials of the earth’s crust. 

Balancing Cuts and Fills. In the construction of new roads, 
the formation of the roadbed consists in bringing the surface of the 
ground to the adopted grade. This grade should be established so as 



































HIGHWAY CONSTRUCTION 


45 


to reduce the earthwork to the least possible amount, both to render 
the cost of construction low, and to avoid unnecessary marring the 
appearance of the country in the vicinity of the road. The most 
desirable position of the grade line is usually that which makes the 
amount of cutting and filling equal to each other, for any surplus 
embankment over cutting must be made up by borrowing, and surplus 
cutting must be wasted, both of these operations involving additional 
cost for labor and land. 

Inclination of Side Slopes. The proper inclination for the 
side slopes of cutting and embankments depends upon the nature of 
the soil, the action of the atmosphere and of internal moisture upon 
it. For economy the inclination should be as steep as the nature 
of the soil will permit. 

The usual slopes in cuttings are: 


Solid rock.1 to 1 

Earth and Gravel.3J to 1 

Clay..3 or 6 to 1 

Fine sand.2 or 3 to 1 


The slopes of embankment are usually made 1J to 1. 

Form of Side Slopes. The natural, strongest, and ultimate 
form of earth slopes is a concave curve, in which the flattest portion 
is at the bottom. This form is very rarely given to the slopes in con¬ 
structing them; in fact, the reverse is often the case, the slopes being 
made convex, thus saving excavation by the contractor and inviting 
slips. 

In cuttings exceeding 10 feet in depth the forming of concave 
slopes will materially aid in preventing slips, and in any case they will 



reduce the amount of material which will eventually have to be re¬ 
moved when cleaning up. Straight or convex slopes will continue 
to slip until the natural form is attained. 

A revetment or retaining wall at the base of a slope will save 
excavation. 













46 


HIGHWAY CONSTRUCTION 


In excavations of considerable depth, and particularly in soils 
liable to slips, the slope may be formed in terraces, the horizontal 
offsets or benches being made a few feet in width with a ditch on 
the inner side to receive the surface water from the portion of the 
side slope above them. These benches catch and retain earth 
that may fall from the slopes above them. The correct forms for the 
slopes of embankment and excavation are shown in Figs. 21 and 22. 

Covering of Slopes. It is not usual to employ any artificial 
means to protect the surface of the side slopes from the action of the 
weather; but it is a precaution which in the end will save much labor 



and expense in keeping the roadways in good order. The simplest 
means which can be used for this purpose consists in covering the 
slopes with good sods, or else with a layer of vegetable mould about 
four inches thick, carefully laid and sown with grass seed. These 
means are amply sufficient to protect the side slopes from injury 
when they are not exposed to any other cause of deterioration than 
the wash of the rain and the action of frost on the ordinary moisture 
retained by the soil. 

A covering of brushwood or a thatch of straw may also be used 
with good effect; but from their perishable nature they will require 
frequent renewal and repairs. 

Where stone is abundant a small wall of stone laid dry may be 
constructed at the foot of the slopes to prevent any wash from them 
being carried into the ditches. 

Shrinkage of Earthwork. All materials when excavated 
increase in bulk, but after being deposited in banks subside or shrink 
(rock excepted) until they occupy less space than in the pit from 
which excavated. 

Rock, on the other hand, increases in volume by being broken 
up, and does not settle again into less than its original bulk. The 
increase may be taken at 50 per cent. 







HIGHWAY CONSTRUCTION 


47 


l lie shrinkage in the different materials is about as follows: 


Gravel. 

. . . 8 

per cent 

Gravel and sand. 

. . . 9 

U (( 

Clay and clay earths. 

. . .10 

Li ( 

Loam and light sandy earths. . . 

. .12 

u a 

Loose vegetable soil. 


U LL 

Puddled clay. 

. .25 

Li LL 


'Thus an excavation of loam measuring 1,000 cubic yards will 
form only about 880 cubic yards of embankment, or an embankment 
of 1,000 cubic yards will require about 1,120 cubic yards measured 
in excavation to make it. A rock excavation measuring 1,000 yards 
will make from 1,500 to 1,700 cubic yards of embankment, depending 
upon the size of the fragments. 

The lineal settlement of earth embankments will be about in 
the ratio given above; therefore either the contractor should be 
instructed in setting his poles to guide him as to the height of grade 
on an earth embankment to add the required percentage to the fill 
marked on the stakes, or the percentage may be included in the 
fill marked on the stakes. In rock embankments this is not necessary. 

Classification of Earthwork. Excavation is usually classi¬ 
fied under the heads earth, hard pan, loose rock, and solid rock. For 
each of these classes a specific price is usually agreed upon, and an 
extra allowance is sometimes made when the haul or distance to 
which the excavated material is moved exceeds a given amount. 

The characteristics which determine the classes to which a given 
material belongs are usually described with clearness in the speci¬ 
fications, as: 

fiarth will include loam, clay, sand, and loose gravel. 

Hardpan will include cemented gravel, slate, cobbles, and boul¬ 
ders containing less than one cubic foot, and all other matters of an 
earthy nature, however compact they may be. 

Loose rock will include shale, decomposed rock, boulders, and 
detached masses of rock containing not less than three cubic feet, 
and all other matters of a rock nature which may be loosened with a 
pick, although blasting may be resorted to in order to expedite the 
work. 


Solid rock will include all rock found in place in ledges 


and 












48 


HIGHWAY CONSTRUCTION 


masses, or boulders measuring more than three cubic feet, and which 
can only be removed by blasting. 

Prosecution of Earthwork. No general rule can be laid 
down for the exact method of carrying on an excavation and dis¬ 
posing of the excavated material. The operation in each case can 
only be determined bv the requirements of the. contract, character 
of the material, magnitude of the work, length of haul, etc. 

Formation of Embankments. Where embankments are to be 
formed of less than two feet in height, all stumps, weeds, etc. should 
be removed from the space to be occupied by the embankment. 
For embankments exceeding two feet in height stumps need only 
be close cut. Weeds and brush, however, ought to be removed and 
if the surface is covered with grass sod, it is advisable to plow a fur¬ 
row at the toe of the slope. Where a cutting passes into a fill all 
the vegetable matter should be removed from the surface before 
placing the fill. The site of the bank should be carefully examined 
and all deposits of soft, compressible matter removed. When a bank 
is to be made over a swamp or marsh, the site should be thoroughly 
drained, and if possible the fill should be started on hard bottom. 

Perfect stability is the object aimed at, and all precautions neces¬ 
sary to this end should be taken. Embankments should be built in 
successive layers, banks two feet and under in layers from six 
inches to one foot, heavier banks in layers 2 and 3 feet thick. The 
horses and vehicles conveying the materials should be required to 
pass over the bank for the purpose of consolidating it, and care 
should be taken to have the layers dip towards the center. Embank¬ 
ments first built up in the center, and afterwards widened by dump¬ 
ing the earth over the sides, should not be allowed. 

Embankments on Hillsides. When the axis of the road 
is laid out on the side slope of a hill, and the road is formed partly 
by excavating and partly by embanking, the usual and most simple 
method is to extend out the embankment gradually along the whole 
line of the excavation. This method is insecure; the excavated 
material if simply deposited on the natural slope is liable to slip, 
and no pains should be spared to give it a secure hold, particularly 
at the toe of the slope. The natural surface of the slope should be 
cut into steps as shown in Figs. 23 and 24. The dotted line AB 




HIGHWAY CONSTRUCTION 


49 


represents the natural surface of the ground, CEB the excavation, 
and ADC the embankment, resting on steps which have been cut 
between A and C. The best position for these steps is perpendicular 
to the axis of greatest pressure. If A D is inclined at the angle of 
repose of the material, the steps near A should be inclined in the 



opposite direction to A D, and at an angle of nearly 90 degrees 
thereto, while the steps near C may be level. If stone is abundant, 
the toe of the slope may be further secured by a dry wall of stone. 

On hillsides of great inclination the above method of construc¬ 
tion will not be sufficiently secure; retaining walls of stone must 
be substituted for the side slopes of both the excavations and em¬ 
bankments. These walls may be made of stone laid dry, when stone 



Fig. 24. Hillside Road with Retaining and Revetment Walls. 


can be procured in blocks of sufficient size to render this kind of con¬ 
struction of sufficient stability to resist the pressure of the earth. 
When the stones laid dry do not offer this security, they must be laid 
in mortar. The wall which forms the slope of the excavation should 
be carried up as high as the natural surface of the ground. Unless 
the material is such that the slope may be safely formed into steps 
or benches as shown in Fig. 23, the wall that sustains the embank¬ 
ment should be built up to the surface of the roadway, and a parapet 












50 


HIGHWAY CONSTRUCTION 


wall or fence raised upon it, to protect pedestrians against accident. 
(See Fig. 24.) 

For the formula for calculating the dimensions of retaining walls 
see instruction paper on Masonry Construction. 

Roadways on Rock Slopes. On rock slopes when the in¬ 
clination of the natural surface is not greater than one perpendicular 
to two base, the road may be constructed partly in excavation and 
partly in embankment in the usual manner, or by cutting the face 
of the slope into horizontal steps with vertical faces, and building 
up the embankment in the form of a solid stone wall in horizontal 
courses, laid either dry or in mortar. Care is required in proportion¬ 
ing the steps, as all attempts to lessen the quantity .of excavation by 
increasing the number and diminishing the width of the steps require 
additional precautions against settlement in the built-up portion 
of the roadway. 

When the rock slope has a greater inclination than 1 :2 the 
whole of the roadway should be in excavation. 

In some localities roads have been constructed along the face 
of nearly perpendicular cliffs on timber frameworks consisting of 
horizontal beams, firmly fixed at one end by being let into holes 
drilled in the rock, the other end being supported by an inclined 
strut resting against the rock in a shoulder cut to receive it. There 
are also examples of similar platforms suspended instead of being 
supported. 

Earth Roads. The term “earth road” is applied to roads 
where the surface consists of the native soil; this class of road is the 
most common and cheapest in first cost. At certain seasons of the 
year earth roads when properly cared for are second to none, but 
during the spring and wet seasons they are very deficient in Jhe im¬ 
portant requisite of hardness, and are almost impassable. 

For the construction of new earth roads, all the principles pre¬ 
viously discussed relating to alignment, grades, drainage, width, etc., 
should be carefully followed. The crown or transverse contour 
should be greater than in stone roads. Twelve inches at the center 
in 25 feet will be sufficient. 

Drainage is especially important, because the material of the 
road is more susceptible to the action of water, and more easily 




HIGHWAY CONSTRUCTION 


51 


destroyed by it than are the materials used in the construction of the 
better class of roads. When water is allowed to stand upon the 
road, the earth is softened, the wagon wheels penetrate it and the 
horses’ feet mix and kneed it until it becomes impassable mud. The 
action of frost is also apt to be more disastrous upon the more per¬ 
meable surface of the earth road, having the effect of swelling and 
heaving the roadway and throwing its surface out of shape. It mav 



Fig. 25. Busli Hooks. 


in fact be said that the whole problem of the improvement and 
maintenance of ordinary country roads is one of drainage. 

In the preparation of the wheelway all stumps, brush, vegetable 
matter, rocks and boulders should be removed from the surface and 
the resulting holes filled in with clean earth. The roadbed having 



been brought to the required grade and crown should be thoroughly 
rolled, all inequalities appearing during the rolling should be filled 
up and re-rolled. 

Care of Earth Roads. If the surface of the roadway is prop¬ 
erly formed and kept smooth, the water will be shed into the side 
ditches and do comparatively little harm; but if it remains upon the 
surface, it will be absorbed and convert the road into mud. All 
ruts and depressions should be filled up as soon as they appear. 
Repairs should be attended to particularly in the spring. At this 
season a judicious use of a road machine and rollers will make a 


















52 


HIGHWAY CONSTRUCTION 


smooth road. In summer when the surface gets roughed up it can 
be improved by running a harrow over it; if the surface is a little 
muddy this treatment will hasten the drying. 

During the fall the surface should be repaired, with special 
reference to putting it in shape to withstand the ravages of winter. 
Saucer-like depressions and ruts should be filled up with clean earth 
similar to that of the roadbed and tamped into place. 

The side ditches should be examined in the fall to see that they 
are free from dead weeds and grass, and late in winter they should 
be examined again to see that they are not clogged. The mouths of 
culverts should be cleaned of rubbish and the outlet of tile drains 
opened. Attention to the side ditches will prevent overflow, and 
washing of the roadway, and will also prevent the formation of ponds 
at the roadside and the consequent saturation of the roadbed. 

Holes and ruts should not be filled with stone, bricks, gravel 
or other material harder than the earth of the roadw T ay as the hard 
material will not wear uniform with the rest of the road, but produce 
bumps and ridges, and usually result in making two holes, each 
larger than the original one. It is bad practice to cut a gutter from 
a hole to drain it to the side of the road. Filling is the proper course, 
whether the hole is dry or contains mud. 

In the maintenance of clay roads neither sods nor turf should 
be used to fill holes or ruts; for, though at first deceptively tough, 
they soon decay and form the softest mud. Neither should the ruts 
be filled with field stones; they will not wear uniformly with the rest 
of the road, but will produce hard ridges. 

Trees and close hedges should not be allowed within 200 feet 
of a day road. It requires all the sun and wind possible to keep its 
surface in a dry and hard condition. 

Sand Roads. The aim in the improvement of sand roads is to 
have the wheelway as narrow and well defined as possible, so as to 
have all the vehicles run in the same track. An abundant growth 
of vegetation should be encouraged on each side of the wheel way, 
for by this means the shearing of the sand is, in a great measure, 
avoided. Ditching beyond a slight depth to carry away the rain 
water is not desirable, for it tends to hasten the drying of the sands 
which is to be avoided. Where possible the roads should be over-' 




HIGHWAY CONSTRUCTION 


53 


hung with trees, the leaves and twigs of which catching on the 
wheelway will serve still further to diminish the effect of the wheels 
in moving the sands about. If clay can be obtained, a boating 6 
inches thick will be found a most effective and economical improve¬ 
ment. A coating of 4 inches of loose straw will, after a few days’ 
travel, grind into the sand and become as hard and as firm as a 
dry clay road. 

The maintaining of smooth surfaces on all classes of earth roads 
will be greatly assisted and cheapened by the frequent use of a'roller 
(either steam or horse) and any one of the various forms of road 
grading and scraping machines. In repairing an earth road the 
plough should not be used. It breaks up the surface which has 
been compacted by time and travel. 

TOOLS FOR GRADING. 

Picks are made of various styles, according to the class of 
material in which they are to be used. Fig. 28 shows the form 




usually employed in street work. Fig. 29 shows the form generally 
used for clay or gravel excavation. 

The eye of the pick is generally formed of wrought iron, pointed 
with steel. The weight of picks ranges from 4 to 9 lb. 



Shovels are made in two forms, square and round pointed, 
usually of pressed steel- 

Ploughs are extensively employed in grading, special forms 
being manufactured for the purpose. They are known as “ grading 
ploughs,” “road ploughs/’ “township ploughs,” etc. They vary 

















54 


HIGHWAY CONSTTCUCTION 


in form according to the kind of work they are intended for, viz.: 
loosening earth, gravel, hardpan, and some of the softer rocks. 

These ploughs are made of great strength, selected white oak, 
rock elm, wrought steel and iron being generally used in their con¬ 
struction. The cost of operating ploughs ranges from 2 to 5 cents 
per cubic yard, depending upon the compactness of the soil. The 
quantity of material loosened will vary from 2 to 5 cubic yards per 
hour. 

Fig. 31 shows the form usually adopted for loosening earth. 
This plough does not turn the soil, but cuts a furrow about 10 



Fig. 31. Grading Plow. 


inches wide and of a depth adjustable up to 11 inches. 

In light soil the ploughs are operated by two or four horses; in 
heavy soils as many as eight are'employed. Grading ploughs vary 
in weight from 100 to 325 lb. 



Fig. 32 illustrates a plough specially designed for tearing up 
macadam, gravel, or similar material. The point is a straight bar 
of cast steel drawn down to a point, and can be easily repaired. 



























HIGHWAY CONSTRUCTION 


55 


Scrapers are generally used to move the material loosened by 
ploughing; they are made of either iron or steel, and in a variety 
of form, and are known by various names, as “ drag, ” “buck,” 
“ pole,” and “ wheeled”. The drag scrapers are usually employed 
on short hauls, the wheeled on long hauls. Fig. 33 illustrates the 
usual form of dr&g scrapers. 

Drag scrapers are made in three sizes. The smallest, for one 
horse, has a capacity of 3 cubic feet; the others, for two horses, 



have a capacity of 5 to 7\ cubic feet. The smallest weighs about 
90 lb., and the larger ones from 94 to 102 lb. 

Buck scrapers are made in two sizes—two-horses, carrying 7 h 
cubic feet; four-horses, 12 cubic feet. 

Pole scraper, Fig. 34, is designed for use in making and leveling 
earth roads and for cutting and cleaning ditches; it is also well 



adapted for moving earth short distances at a minimum cost. 

Wheeled scrapers consist of a metal box, usually steel, mounted 
on wheels, and furnished with levers for raising, lowering, and 
































56 


HIGHWAY CONSTRUCTION 


dumping. They are operated in the same manner as drag scrapers, 
except that all the movements are made by means of the levers, and 
without stopping the team. By their use the excessive resistance to 



traction of the drag scraper is avoided. Various sizes are made, 
ranging in capacity from 10 to 17 cubic feet. In weight they range 
from 350 to 700 lb. 

Wheelbarrows. The wheelbarrow shown in Fig. 30 is con¬ 
structed of wood and is the most commonly employed for earth¬ 
work. Its capacity ranges from 2 to 2\ cubic feet. Weight about 
50 lb. 

The barrow, Fig. 37, has a pressed-steel tray, oak frame, and 
steel wheel, and will be found more durable in the maintenance 



department than the all wood barrow. Capacity from 3J to 5 cubic 
feet, depending on size of tray. 

The barrow, Fig. 38, is constructed with tubular iron frames 
and steel tray, and is adaptable to the heaviest work, such as 













































HIGHWAY CONSTRUCTION 


57 


moving heavy broken stone, etc., or it may be employed with ad¬ 
vantage in the cleaning department. Capacity from 3 to 4 cubic 
feet. Weight from 70 to 82 lb. 



The maximun distance to which earth can be moved economic¬ 
ally in barrows is about 200 feet. The wheeling should be per¬ 
formed upon planks, whose steepest inclination should not exceed 1 
in 12. The force required to move a barrow on a plank is about Ag- 
part of the weight; on hard dry earth, about T J T part of the weight. 



Fig. 38. Metal Barrow. 


The time occupied in loading a barrow will vary with the 
character of the material and the proportion of wheelers to shovel¬ 
lers. Approximately, a shoveller takes about as long to fill a barrow 
with earth as a wheeler takes to wheel a full barrow a distance of 
about 100 or 120 feet on a horizontal plank and return with the 
empty barrow. 

Carts. The cart usually employed for hauling earth, etc., is 
shown in Fig. 39. The average capacity is 22 cubic feet, and the 
average weight is 800 lb. These carts are usually furnished with 
broad tires, and the body is so balanced that the "load is evenly 
divided about the axle. 













58 


HIGHWAY CONSTRUCTION 


The time required to load a cart varies with the material. One 
shoveller will require about as follows: Clay, seven minutes; loam, 
six minutes; sand, five minutes. 



Fig. 39. Earth Wagon. 


Dump Cars. These cars are made to dump in several different 
ways, viz., single or double side, single or double end, and rotary 
or universal dumpers. 

Dump cars may be operated singly or in trains, as the magni¬ 
tude of the work may demand. They may be moved by horses or 



Fig. 40. Dump Cart. 

small locomotives. They are made in various sizes, depending upon 
the gauge of the track on which they are run. A common gauge is 





















































































HIGHWAY CONSTRUCTION 


59 


20 inches, but it varies from that up to the standard railroad gauge 
of 56J inches. 

Dump Wagons. (Fig. 40.) The use of these wagons for mov¬ 
ing excavated earth, etc., and for transporting materials such as sand, 
gravel, etc., materially shortens the time required for unloading the 
ordinary form of contractor’s wagon; having no reach or pole con¬ 
necting the rear axle with the center bearing of the front axle, they 
may be cramped short and the load deposited just where required. 
They are operated by the driver, and the capacity ranges from 35 
to 45 cubic feet. 

Mechanical Graders are used extensively in the making and 
maintaining of earth roads. They excavate and move earth more 
expeditiously and economically than can be done by hand; they are 
called by various names, such as “road machines,” “graders,” 
“road hones,” etc. Their general form is shown in Fig. 41. 

Briefly described, they consist of a large blade made entirely 
of steel or of iron, or wood shod with steel, which is so arranged by 
mechanism attached to the frame from which it is suspended that it 
can be adjusted and fixed in any direction by the operator. In their 
action they combine the work of excavating and transporting the 



Fig. 41. Mechanical Grader. 


earth. They have been chiefly employed in the forming and main¬ 
tenance of earth roads, but may be also advantageously used in pre¬ 
paring the subgrade surface of roads for the reception of broken 
stone or other improved covering. 

A large variety of such machines are on the market. The 
“New Era” grader excavates the material from side ditches, and 









60 


HIGHWAY CONSTRUCTION 


automatically loads the material into carts or wagons. Briefly de¬ 
scribed, the machine consists of a plough which loosens and raises 
the earth, depositing it upon a transverse carrying-belt, which con¬ 
veys it from excavation to embankment. This carrier is built in four 
«/ 

sections, bolted together, so it can be used to deliver earth at 14, 
17, 19, or 22 feet from the plough. The carrier belt is of heavy 
3-ply rubber 3 feet wide. 

The plough and carrier are supported by a strong trussed frame¬ 
work resting on heavy steel axles and broad wheels. The large 
rear wheels are ratcheted upon the axle, and connected with strong 
gearing which propels the carrying-belt at right angles to the direc¬ 
tion in which the machine is moving;. 

The wheels and trusses are low and broad, occupying a space 
8 feet wide and 14 feet long, exclusive of the side carrier. This 
enables it to work on hillsides where any wheeled implements can 
be used. Notwithstanding its large size it is so flexible that it may 
be turned around on a 16-foot embankment. Pilot wheels and 
levers enable the operator to raise or lower the plough or carrier at 
pleasure. 

As a motive power 12 horses—8 driven in front, 4 abreast, and 
4 in the rear on a push cart—are usually employed. 

When the teams are started, the operator lowers the plough and 
throws the belting into gear, and as the plough raises and turns the 
earth to the side the belt receives and delivers it at the distance for 
which the carrier is adjusted, forming either excavation or embank¬ 
ment. 

When it becomes necessary to deliver the excavated earth beyond 
the capacity of the machine (22 feet or 74 feet above the plough), 
the earth is loaded upon wagons, then conveyed to any distance. 
Arranging the carrier at 19 feet, wagons are driven under the car¬ 
rier and loaded with 1J to \\ yards of earth in from 20 to 30 
seconds. When one wagon turns out with its load, another drives 
under the carrier, and the machine thus loads 600 to 800 wagons 
per day. It is claimed that with six teams and three men it is capa¬ 
ble of excavating and placing in embankment from 1000 to 1500 
cubic yards of earth in ten hours, or of loading from 600 to 800- 



HIGHWAY CONSTRUCTION 


61 


wagons in the same time, and that the cost of this handling is from 
LV to 2\ cents per cubic yard. 

Points to be Considered in Selecting a Road Machine. In 

the selection of a road machine the following points should be care¬ 
fully considered: 

(1) Thoroughness and simplicity of its mechanical construction. 

(2) Material and workmanship used in its construction. 

(3) Ease of operation. 

(4) Lightness of draft. 

(5) Adaptability for doing general road-work, ditching, etc. 

(6) Safety to the operator. 

Care of Road Machines. The road machine when not in use 
should be stored in a dry house and thoroughly cleaned, its blade 
brushed clean from all accumulations of mud, wiped thoroughly dry, 
and well covered with grease or crude oil. The axles, journals, and 
wearing parts should be kept well oiled when in use, and an extra 
blade should be kept on hand to avoid stopping the machine while 
the dulled one is being sharpened. 

Surface Graders. The surface grader, Fig. 42, is used for re¬ 
moving earth previously loosened by a plough. It is operated by 
one horse. The load may be retained and carried a considerable 



Fig. 42. Surface Gi*ader. 

distance, or it may be spread gradually as the operator desires. It 
is also employed to level off and trim the surface after scrapers. 

The blade is of steel, J-inch thick, 15 inches wide, and 30 
inches long. The beam and other parts are of oak and iron. 
Weight about 60 lb. 








62 


HIGHWAY CONSTRUCTION 


The road leveller, Fig. 43, is used for trimming and smoothing 
the surface of earth roads. It is largely employed in the Spring 
when the frost leaves the ground. 



Fig. 43. Road Leveller. 



The blade is of steel, J-inch thick by 4 inches by 72 inches, and 
is provided with a seat for the driver. It is operated by a team of 
horses. Weight about 150 lb. 

























HIGHWAY CONSTRUCTION 


63 


Draining=tools. The tools employed for digging the ditches 

and shaping the bottom to fit the drain tiles are shown in Fig. 44. 

They are convenient to use, and expedite the work by avoiding 

unnecessarv excavation. 

«/ 

The tools are used as follows: Nos. 3, 4 and 5 are, used for 
digging the ditches; Nos. 6 and 7 for cleaning and rounding the 



♦ 


Fig. 45. Reversible Roller. 

bottom of the ditch for round tile. No. 2 is used for shoveling out 
loose earth and levelling the bottom of the ditch; No. 1 is used for 
the same purpose when the ditch is intended for “sole ” tile. 



Fig. 46. AVatering Cart. 


Horse Rollers. There is a variety of horse rollers on the 
market. Fig. 45 shows the general form. Each consists essentially 
of a hollow cast-iron cylinder 4 to 5 feet long, 5 to 6 feet in 































64 


HIGHWAY CONSTRUCTION 


diameter, and weighing from 3 to 6 tons. Some forms are provided 
with boxes in which stone or iron may be placed to increase the 
weight, and some have closed ends and may be filled with water or 
sand. 

Sprinkling=carts. Fig. 46 shows a convenient form of sprink¬ 
ling cart for suburban streets and country roads. Capacity about 
150 gallons. 

ROAD COVERINGS. 

Road coverings consist of some foreign material as gravel, 
broken stone, clay, etc., placed on the surface of the earth road. 
The object of this covering, whatever its nature, is (1) to protect the 
natural soil from the effect of weather and travel, and (2) to furnish 
a smooth surface on which the resistance to traction will be reduced 
to the least possible amount, and over which vehicles may pass with 
safety and expedition at all seasons of the year. Where an artificial 
covering is employed, the wheel loads coming upon its surface are 
distributed over a greater area of the roadbed than if the loads 
come directly upon the earth itself. The loads are not sustained by 
the covering as a rigid structure, but are transferred through it to 
the roadbed, which must support both the weight of the covering 
and the load coming upon it. 

Gravel Roads. Gravel is an accumulation of small more or 
less rounded stones which usually vary from the size of a small pea 
to a walnut. It is often intermixed with other substances, such as 
sand, clay, loam, etc., from each of which it derives a distinctive 
name. In selecting gravel for road purposes the chief quality to be 
sought for is the property of binding. 

Gravel in general is unserviceable for roadmaking. This is 
due mainly to the fact that the surface of the pebbles is smooth, so 
that they will not bind together in the manner of broken stone. 
There is also an absence of dust or other material to serve as a 
binder, and even if such binding material is furnished it is difficult 
to effectively hold the rounded and polished surface of the pebbles 
together. 

In certain deposits of gravel, particularly where the pebbly 
matter is to a greater or less extent composed of limestone, a con¬ 
siderable amount of iron oxide has been gathered in the mass. 



HIGHWAY CONSTRUCTION 


65 


This effect is due to the tendency of water which contains iron to 
lay down that substance and to take lime in its place when the 
opportunity for so doing occurs. Such gravels are termed ferru¬ 
ginous. They are commonly found in a somewhat cemented state, 
and when broken up and placed upon roads they again cement, even 
more firmly than in the original state, often forming a roadway of 
very good quality. 

When no gravel but that found in rivers or on the seashore can 
be obtained, one-half of the stone should be broken and mixed with 
the other half; to the stone so mixed a small quantity of clay or 
loam, about one-eighth of the bulk of the gravel, must be added: 
an excess is injurious. Sand is unsuitable. It prevents packing in 
proportion to the amount added. 

Preparing the Gravel. Pit gravel usually contains too much 
earth, and should be screened before being used. Two sieves should 
be provided, one with meshes of one and one-half inches, so that all 
pebbles above that size may be rejected, the other with meshes of 
three quarters of an inch, and the material which passes through it 
should be thrown away. The expense of screening will be more 
than repaid by the superior condition of the road formed by the 
cleaned material, and by the diminution of labor in keeping it in 
order. The pebbles larger than one and a half inches may be 

broken to that size and mixed with clean material. 

\ 

Laying the Gravel. On the roadbed properly prepared a layer 
of the prepared gravel four inches thick is uniformly spread over the 
whole width, then compacted with a roller weighing not less than 
two tons, and having a length of not less than thirty inches. The 
rolling must be continued until the pebbles cease to rise or creep in 
front of the roller. The surface must be moistened by sprinkling 
in advance of the roller, but too much water must not be used. 
Successive layers follow, each being treated in the above described 
manner until the requisite depth and form has been attained. 

The gravel in the bottom layer must be no larger than that in 
the top layer; it must be uniformly mixed, large and small together, 
for if not, the vibration of the traffic and the action of frost will 
cause the larger pebbles to rise to the surface and the smaller ones 
to descend, and the road will never be smooth or firm. 





66 


HIGHWAY CONSTRUCTION 


The pebbles in a gravel road are simply imbedded in a paste 
and can be easily displaced. It is for this reason, among others, 
that such roads are subject to internal destruction. 

The binding power of clay depends in a large measure upon 
the state of the weather. During rainy periods a gravel road be¬ 
comes soft and muddy, while in very dry weather the clay will con¬ 
tract and crack, thus releasing the pebbles, and giving a loose 
surface. The most favorable conditions are obtained in moderately 
damp or dry weather, during which a gravel road offers several 
advantages for light traffic, the character of the drainage, etc., 
largely determining durability, cost, maintenance, etc. 

Repair. Gravel roads constructed as above described will 
need but little repairs for some years, but daily attention is required 
to make these. A garden rake should be kept at hand to draw 
any loose gravel into the wheel tracks, and for filling any depres¬ 
sions that may occur. 

In making repairs, it is best to apply a small quantity of gravel 
at a time, unless it is a spot which has actually cut through. Two 
inches of gravel at once is more profitable than a larger amount. 
Where a thick coating is applied at once it does not all pack, and if, 
after the surface is solid, a cut be made, loose gravel will be found; 
this holds water and makes the road heave and become spoutv 
under the action of frost. It will cost no more to apply six inches 
of gravel at three different times than to do it at once. 

At every one-eighth of a mile a few cubic yards of gravel 
should be stored to be used in filling depressions and ruts as fast as 
they appear, and there should be at least one laborer to every five 
miles of road. 

Broken Stone Roads. Broken stone roads are formed by pla¬ 
cing small angular fragments of stone on the surface of the earth 
roadbed and compacting into a solid mass by rolling. This class 
of road covering is generally called a Macadam or Telford road 
from the name of the two men who first introduced this type into 
England. 

The name of Telford is associated with a rough stone founda¬ 
tion, which he did not always use, but which closely resembled that 
which had been previously used in France. Macadam disregarded 




HIGHWAY CONSTRUCTION 


67 


this foundation, contending that the subsoil, however bad, would 
carry any weight if made dry by drainage and kept dry by an im¬ 
pervious covering. The names of both have ever since been 
associated with the class of road which each favored, as well as with 
roads on which all their precepts have been disregarded. 

Quality of Stones. The materials used for broken-stone pave¬ 
ments must of necessity vary very much according to the locality. 
Owing to the cost of haulage, local stone must generally be used, 
especially if the traffic be only moderate. If, however, the traffic is 
heavy, it will sometimes be found better and more economical to 
obtain a superior material, even at a higher cost, than the local 
stone; and in cases where the traffic is very great, the best material 
that can be obtained is the most economical. 

The qualities required in a good road stone are hardness and 
and toughness and ability to resist the disintegrating action of the 
weather. These qualities are seldom found together in the same 
stone. Igneous and siliceous rocks, although frequently hard and 
tough, do not consolidate so well nor so quick as limestone, owing 
to the sandy detritus formed by the two first having no cohesion, 
whilst the limestone has a detritus which acts like mortar in binding 
the stones together. 

A stone of good binding nature will frequently wear much 
better than one without, although it is not so hard. A limestone 
road well made and of good cross-section will be more impervious 
than any other, owing to this cause, and will not disintegrate so 
soon in dry weather, owing partly to this and partly to the well- 
known quality which all limestone has of absorbing moisture from 
the atmosphere Mere hardness without toughness is not of much 
use, as a stone may be very hard but so brittle as to be crushed to 
powder under a heavy load, while a stone not so hard but having a 
greater degree of toughness will be uninjured. 

By a stone of good binding quality is meant one that, when 
moistened by water and subjected to the pressure of loaded wheels 
or rollers, will bind or cement together. This quality is possessed to 
a greater or less extent by nearly all rocks when in a state of dis¬ 
integration. The binding is caused by the action of water upon the 
chemical constituents of the stone contained in the detritus produced 






68 


HIGHWAY CONSTRUCTION 


by crushing the stone, and by the friction of the fragments on each 
other while being compacted; its strength varies with the different 
species of rock, but it exists in some measure with them all, being 
greatest with limestone and least with gneiss. 

The essential condition of the stone to produce this binding 
effect is that it be sound. No decayed stone retains the property of 
binding, though in some few cases, where the material contains iron 
oxides, it may, by the cementing property of the oxide, undergo a 
certain binding. 

A stone for a road surface should be as little absorptive of 
moisture as possible in order that it may not suffer injury from the 
action of frost. Many limestones are objectionable on this account. 

The stone used should be uniform in quality, otherwise it will 
wear unevenly, and depressions will appear where the softer material 
has been used. 

As the under parts of the road covering are not subject to the 
wear of traffic, and have only the weight of loads to sustain, it is 
not necessary that the stone of the lower layer be so hard or so 
tough as the stone for the surface, hence it is frequently possible by 
using an inferior stone for that portion of the work, to greatly reduce 
the cost of construction. 

Size of Stones. The stone should be broken into fragments 
as nearly cubical as possible. The size of the cubes will depend 
upon the character of the rock. If it be granite or trap, they should 
not exceed 1^ inches in their greatest dimensions; if limestone, they 
should not exceed 2 inches. 

The smaller the stones the less the percentage of voids. Small 
stones compact sooner, require less binding, and make a smoother 
surface than large ones, but the size of the stone for any particular 
section of a road must be determined to a certain extent by the 
amount of traffic which it will have to bear and the character of the 
rock used. 

It is not necessary nor is it advisable that the stone should be 
all of the same size; they may be of all sizes under the maximum. 
In this condition the smaller stones fill the voids between the larger 
and less binding is required. 

Thickness of the Broken Stone. The offices of the broken 



HIGHWAY CONSTRUCTION 


69 


stone are to endure friction and to shed water; its thickness must 
be regulated by the quality of the stone, the amount of traffic, and 
nature of the natural soil bed. Under heavy traffic it is advisable 
to make the thickness greater than for light traffic, in order to pro¬ 
vide for wear and lessen the cost of renewals. 

When the roadbed is firm, well drained, and not likely to be 
affected by ground water, it will always afford a firm foundation 
for the broken stone, the thickness of which may be made the mini¬ 
mum for good construction. This thickness is four inches. When 
this thickness is employed the stone must be of exceptionally fine 
quality and the road must be maintained by the “ continuous ” 
method. With heavy traffic the thickness should be increased over 
the minimum a certain amount, say 2 inches, to provide for wear. 
Where the foundation is unstable and there is a tendency on the 
part of the loads to break through the covering, the thickness of 
the stone must be made the maximum, which is 12 inches. In such 
a case it may be advisable to employ a Telford foundation. Where 
the covering exceeds six inclies in thickness, the excess may be 
composed of gravel, sand or ledge stone, the choice depending 
entirely on the cost, for all are equally effective. 

Foundation. The preparation of the natural soil over which 
the road is to be constructed, to enable it to sustain the superstruc¬ 
ture and the weights brought upon it, requires the observance of 
certain precautions the neglect of which will sooner or later result 
in the deterioration or possible destruction of the road covering. 
These precautions vary with the character of the soil. 

Soils of a siliceous and calcareous nature do not present any 
great difficulty, as their porous nature generally affords good natural 
drainage which secures a dry foundation. Their surface, however, 
requires to be compacted; this is effected by rolling. 

The rolling should be carried out in dry weather, and any de¬ 
pressions caused by the passage of the roller should be filled with 
the same class of material as the surrounding soil. The rolling 
must be repeated until a uniform and solid bed is obtained. 

The argillaceous and allied soils, owing to their retentive 
nature, are very unstable under the action of water and frost, and 
in their natural condition afford a poor foundation. The prepara- 



70 


HIGHWAY CONSTRUCTION 


tion of such soil is effected by drainage and by the application of a 
layer of suitable material to entirely separate the surface from the 
road material. This material may be sand, furnace ashes or other 
material of a similar nature, spread in a layer from 3 to 6 inches 
thick over the surface of the natural soil. 

When the road is formed in rock cuttings it is advisable to 
spread a layer of sand or other material of light nature, so as to 
fill up the irregularities of the surface as well as to form a cushion 
for the road material to rest on. 

Spreading the Stone. The stone should be hauled upon the 
roadbed in broad-tire two-wheeled carts and dumped in heaps and 
be spread evenly with a rake in a layer which should be of a depth 
of 4J inches. 

Watering. Wetting the stone expedites the consolidation, 
decreases crushing under the roller, and assists the filling of the 
voids with the binder. It should be applied by a sprinkler and 
should not be thrown on in quantity or from the plain nozzle of a 
hose. 

Excessive watering, especially in the earlier stages, tends to 

* 

soften the foundation, and care should be exercised in its appli¬ 
cation. 

Binding. As the voids in loosely spread broken stone range 
from 35 to 50 per cent of the volume, and as no amount of rolling 
will reduce the voids more than one-half, it is necessary, in order to 
form an impervious and compact mass, to add some fine material 
which is called the binder. It may consist of the fragments and 
detritus obtained in crushing the stone. When this is insufficient, 
as will be the case with the harder rocks, the deficiency may be 
made up of clean sand or gravel. The proportion of binder 
should slightly exceed the voids in the aggregate; it must not be 
mixed with the stones, but should be spread uniformly in small 
quantities over the surface and rolled into the interstices with the 
aid of water and brooms. 

As the quality of the binding used is of vital importance, the 
employment of inferior material, such as road scrapings or material 
of a clayey nature, should be avoided, even if the initial cost of the 
work should be greater when a good binding material is used. 




HIGHWAY CONSTRUCTION 


71 


Stone consolidated with improper binding material may present 
a good appearance immediately after being rolled and be otherwise 
an apparently good piece of work, still in damp weather a consider¬ 
able amount of “licking up” by the wheels of the vehicles will take 
place, which reduces the strength of the coating and causes the sur¬ 
face to wear unequally. 

By the application of an immoderate quantity of binding of any 
description the stone coating will become unsound or rotten in con¬ 
dition, and if the binding be of an argillaceous nature, it will expand 
during frost, owing to its absorbent properties, and cause the dis¬ 
placement of the stones. The surface will become sticky, which 
seriously affects the tractive power of horses, while the road itself 
will suffer by the irregular deterioration of the surface. 

The use of such material as mentioned for binding enables 
rolling to be accomplished in much less time than when proper bind¬ 
ing is used, and the cost of consolidating the stone may be reduced 
by 25 per cent; but, on the other hand, the stone coating which will 
probably contain under these circumstances from 30 to 40 per cent 
of soft and soluble matter, and possibly present a smooth surface 
immediately after being rolled, will quickly become “cupped” by 
the wheel traffic, a bumpy surface being the result. This is caused 
by the irregular wear, while the lasting qualities or “life” of the 
coating will be shortened, giving unsatisfactory results to those 
traveling over the road, and the work of renewing the surface of 
the road in this manner may prove a failure on economical grounds. 
There can be no doubt, and it is now being more generally recog¬ 
nized, that sand as a material for binding in connection with rolling 
operations, when applied in a limited but sufficient quantity, pro¬ 
motes the durability of the stone coating, while the general results 
are equally satisfactory; a firm, compact, and smooth surface is 
obtained, and the subsequent maintenance of the road is minimized. 

A great amount of rolling is necessary when sand is employed 
as a binding material, but economy is promoted, and the results are 
more satisfactory when sand is used than by the use of the material 
which gives to the stone an appearance only of having been properly 
consolidated. If clean sand be used in combination with the screen¬ 
ings from the crusher a very satisfactory surface will be obtained. 




72 


HIGHWAY CONSTRUCTION 


If the use of motor vehicles equipped with pneumatic tires be¬ 
comes general, it is possible that some other description of binding 
material will be necessary. The pumping action of suction created 
by pneumatic tires, especially when propelled at a high speed, causes 
a considerable movement of the fine particles of the binding material, 
which on being displaced will convert the covering into a mass of 
stones. This objection can probably be overcome by watering. 

Compacting the Broken Stone. Three methods of compacting 
the broken stone are practiced: (1) by the traffic passing over the road; 

(2) by rollers drawn by horses; (3) by rollers propelled by steam. 

The first method is both defective and objectionable. (1) It is 
destructive to the horses and vehicles using the road. (2) It is waste¬ 
ful of material; about one-third of the stone is worn away in the oper¬ 
ation. (3) Dung and dust are ground up with the stone, and the 
road is more readily affected by wet and frost. 

Steam=rollers were first successfully introduced in France in 1860, 
since which time they have been almost universally adopted on account 
of the superiority and economy of the work done. Their use shortens 
the time required for construction or repair, and effects an indirect 
saving by the reduced wear and tear of horses and vehicles. They are 
made in different weights ranging from 3 to 30 tons. For the compact¬ 
ing of broken stone roads the weights in favor are from ten to fifteen 
tons; the heavier weights are considered unwieldy and their use is 
liable to cause damage to the underground structures that may be in 
the roadway. 

The advantage of steam rolling may be summed up as follows: 

(1) They shorten the time of construction. 

(2) A saving of road material, (a) because there are no loose 
stones to be kicked about and worn; (b) because there is no abrasion 
of the stone, only one surface of the stone being exposed to wear; (c) 
because a thinner coating of stone can be employed; (d) because no 
ruts can be formed in which water can lie to rot the stone. 

(3) Steam-rolled roads are easier to travel on account of their 
even surface and superior hardness and they have a better appearance. 

(4) The roads can be repaired at any season of the year. 

(5) Saving both in materials and manual labor. 




HIGHWAY CONSTRUCTION 

PART II 

STREETS AND HIGHWAYS 

CITY STREETS 

The first work requiring the skill of the engineer is to lay out town 
sites properly, especially with reference to the future requirements of a 
large city where any such possibility exists. Few if any of our large 
cities were so planned. The same principles, to a limited extent, are 
applicable to all towns or cities. The topography of the site should be 
carefully studied, and the street lines adapted to it. These lines 
should be laid out systematically, with a view to convenience and 
comfort, and also with reference to economy of construction, future 
sanitary improvements, grades, and drainage. 

Arrangement of City Streets. Generally, the best method of 
laying out streets is in straight lines, with frequent and regular inter¬ 
secting streets, especially for the business parts of a city. When there 
is some centrally located structure, such as a courthouse, city hall, 
market, or other prominent building, it is very desirable to have several 
diagonal streets leading thereto. In the residence portions of cities, 
especially if on hilly ground, curves may with advantage replace 
straight lines, by affording better grades at less cost of grading, and by 
improving property through avoiding heavy embankments or cuttings. 

Width of Streets. The width of streets should be proportioned 
to the character of the traffic that will use them. No rule can be laid 
down by which to determine the best width of streets; but it may safely 
be said that a street which is likely to become a commercial thorough¬ 
fare should have a width of not less than 120 feet between the building 
lines—the carriage-way 80 feet wide, and the sidewalks each 20 feet 
wide. 

In streets occupied entirely by residences a carriage-way 32 feet 
wide will be ample, but the width between the building lines may be as 
great as desired. The sidewalks may be any amount over 10 feet 



74 


HIGHWAY CONSTRUCTION 


which fancy dictates. Whatever width is adopted for them, not more 
of it than 8 feet need be paved, the remainder being occupied with 
grass and trees. 

Street Grades. The grades of city streets depend upon the 
topography of the site. The necessity of avoiding deep cuttings or 
high embankments which would seriously affect the value of adjoining 
property for building purposes, often demands steeper grades than 
are permissible on country roads. Many cities have paved streets 
on 20 per cent grades. In establishing grades through unimproved 
property, they may usually be laid with reference to securing the most 
desirable percentage within a proper limit of cost. But when improve¬ 
ments have already been made and have been located with reference 
to the natural surface of the ground, giving a desirable grade is fre¬ 
quently a matter of extreme difficulty without injury to adjoining 
property. In such cases it becomes a question of how far individual 

interests shall be sacrificed to the 
general good. There are, how¬ 
ever, certain conditions which it is 
important to bear in mind: 

(1) That the longitudinal 
crown level should be uniformly 
sustained from street to street 
intersection, whenever practicable. 

(2) That the grade should 
be sufficient to drain the surface. 

(3) That the crown levels at 
all intersections should be ex¬ 
tended transversely,to avoid form¬ 
ing a depression at the junction. 

Arrangements of Grades at Street Intersections. The best ar¬ 
rangement for intersections of streets when either or both have much 
inclination, is a matter requiring much consideration, and is one upon 
which much diversity of opinion exists. No hard or fast rule can be 
laid down; each will require special adjustment. The best and sim¬ 
plest method is to make the rectangular space aaaaaaaa, Fig. 47, 
level, with a rise of one-half inch in 10 feet from AAAA to B, placing 
gulleys at AAAA and the catch basins at ccc. When this method is 
not practicable, adopt such a grade (but one not exceeding 2^V per cent) 







R\' 

sS 

J 





| 



a - 

a 


'CxWWWX 

i 

1 

-1 

A 

/ 

i 


i 

1 

a 

A / 

/ 

<7| 

1 

| 

\ 

/ 

' 


1 

1 

1 

| 

✓ 

/ 

/ 

ys 

\ 

\ 

1 

1 

1 

1 

o\ 

i 

i 

At (s' 

V 

.1 

<7, 




s~\ 

a 

1 

1 

1 


I 





1 


Fig. 47. 



























HIGHWAY CONSTRUCTION 


75 


that the rectangle AAAA shall appear to be nearly level; but to secure 
this it must actually have a considerable dip in the direction of the 
slope of the street. If steep grades are continued across intersections, 
they introduce side slopes in the streets thus crossed, which are trouble¬ 
some, if not dangerous, to vehicles turning the corners, especially the 
upper ones. Such intersections are especially objectionable in rainy 



Fig. 48. 


weather. The storm water will fall to the lowest point, concentrating 
a large quantity of water at two receiving basins, which, with a broken 
grade, could be divided between four or more basins. 

Fig. 48 shows the arrangement of intersections in steep grades 
adapted for the streets of Duluth, Minn. From this it will be. seen 
that at these intersections the grades are flattened to three per cent for 
the width of the roadway of the intersecting streets, and that the grade 
of the curbs is flattened to eight per cent for the width of the intersecting 
sidewalks. Grades of less amount on roadway or sidewalk are con¬ 
tinuous. The elevation of block-corners is found by adding together 
the curb elevations at the faces of the block-corners, and 24 per cent of 


























































76 


HIGHWAY CONSTRUCTION 


the sum of the widths of the two sidewalks at the comer, and dividing 
the whole by two. This gives an elevation equal to the average eleva¬ 
tion of the curbs at the corners, plus an average rise of two and one- 
half per cent across the width of the sidewalk. 

Accommodation summits have to be introduced between street 
intersections—first, in hilly localities, to avoid excessive excavation; 
and second, when the intersecting streets are level or nearly so, for the 
purpose of obtaining the fall necessary for surface drainage. 

The elevation and location of these summits may be calculated 
as follows: Let A be the elevation of the highest corner; B, the eleva¬ 
tion of the lowest corner; D, the distance from corner to coi*ner; 
and R, the rate of the accommodation grade. The elevation of the 
summit is equal to 

D’ R + A + B . 

2 

The distance from A or B is found by subtracting the elevation of 
either A or B from this quotient, and dividing the result by the rate 
of grade. Or the summits may be located mechanically by specially 
prepared scales. Prepare two scales divided to correspond to the rate 
of grade; that is, if the rate of grade be 1 foot per 100 feet, then one 
division of the scale should equal 100 feet on the map scale. These 
divisions may be subdivided into tenths. One scale should read from 
right to left, and one from left to right. 

To use the scales, place them on the map so that their figures 
correspond with the corner elevations; then, as the scales read in op- 

Curb _ Lei' e ]— 

" " for tom of Gutter ~~ -* 

Fig. 49. 

posite directions, there is of course some point at which the opposite 
readings will be the same: this point is the location of the summits; 
and the figures read off the scale its elevation. If the difference in 
elevation of the corners is such as not to require an intermediate sum¬ 
mit for drainage, it will be apparent as soon as the scales are placed 
in position. 

When an accommodation summit is employed, it should be form¬ 
ed by joining the two straight grade lines by a vertical curve, as 







HIGHWAY CONSTRUCTION 


77 


described in Part I. The curve should be used both in the crown of 
the street and in the curb and footpath. 

Where the grade is level between intersections, sufficient fall for 
surface drainage may be secured without the aid of accommodation 
summits, by arranging the grades as shown in Fig. 49. The curb is 
set level between the corners; a summit is formed in the gutter; and 
receiving basins are placed at each corner. 

Transverse Grade. In transverse grade the street should be 
level; that is, the curbs on opposite sides should be at the same level, 
and the street crown rise equally from each side to the center. But in 
hillside streets this condition cannot always be fulfilled, and opposite 





sides of the street may differ as much as five feet; in such cases the 
engineer will have to use his discretion as to whether he shall adopt a 
straight slope inclining to the lower side, thus draining the whole street 
by the lower gutter, or adopt the three-curb method and sod the slope 
of the higher side. 

In the improvement of old streets with the sides at different levels, 
much difficulty will be met, especially where shade trees have to be 
spared. In such cases, recognized methods have to be abandoned, and 
the engineer will have to adopt methods of overcoming the difficulties 
in accordance with the conditions and necessities of each particular 
case. Figs. 50, 51, and 52 illustrate several typical arrangements in 



























78 


HIGHWAY CONSTRUCTION 


the case of streets in which the opposite sides are at different levels. 

Transverse Contour or Crown. The reason for crowning a pave¬ 
ment— i. e., making the center higher than the sides—is to provide 
for the rapid drainage of the surface. The most suitable form for the 
crown is the parabolic curve, which may be started at the curb line, 
or at the edge of the gutter adjoining the carriage-way about one foot 



Fig. 53. 


from the curb. Fig. 53 shows this form, which is obtained by dividing 
the ordinate or width from the gutter to the center of the street into ten 
equal parts, and raising perpendiculars the length of which will be 
determined by multiplying the rise at the center by the respective 
number of each perpendicular in the diagram. The amounts thus 
obtained can be added to the rod readings; and the stakes, set at the 
proper distance across the street, with their tops at this level, will give 
the required curve. 

The amount of transverse rise, or the height of the center above 
the gutters, varies with the different paving materials, smooth pave¬ 
ments requiring the least, and rough ones and earth the greatest. The 
rise is generally stated in a proportion of the width of the carriage-way. 
The most suitable proportions are: 

Stone blocks, rise at center, width of carriage-way. 

Wood ” ” ” ” ” 

Brick ” ” ” ” E V ” 

Asphalt ” ” ” ” *V ” 

Sub-Foundation Drainage of Streets. The sub-foundation 

drainage of streets cannot be effected by transverse drains, because of 
their liability to disturbance by the introduction of gas, water, and 
other pipes. 

Longitudinal drains must be depended upon entirely; they may 
be constructed of the same materials and in the same manner as road 
drains. The number of these longitudinal drains must depend upon 








HIGHWAY CONSTRUCTION 


79 


the character of the soil. If the soil is moderately retentive, a single 
row of tiles or a hollow invert placed under the sewer in the center of 
the street will generally be sufficient; or two rows of tiles may be em¬ 
ployed, one placed outside each curb line; if, on the other hand, the 
soil is exceedingly wet and the street very wide, four or more lines 
may be employed. These drains may be permitted to discharge into 
the sewers of the transverse streets. 

Surface Drainage. The removal of water falling on the street 
surface is provided for by collecting it in the gutters, from which it is 
discharged into the sewers or other channels by means of catch-basins 
placed at all street intersections and dips in the street grades. 

Gutters. The gutters must be of sufficient depth to retain all the 
water which reaches them and prevent its overflowing on the footpath. 
The depth should never be less than 6 inches, and very rarely need be 
more than 10 inches. 

Catch=basins are of various forms, usually circular or rectangular, 
built of brick masonry coated with a plaster of Portland cement. 
Whichever form is adopted, they should fulfil the following conditions: 

(1) The inlet and outlet should have sufficient capacity to receive 
and discharge all water reaching the basin. 

(2) The basins should have sufficient capacity below the outlet 
to retain all sand and road detritus, and prevent it being carried into 
the sewer. 

(3) They should be trapped so as to prevent the escape of sewer 
gas. (This requirement is frequently omitted, to the detriment of 
the health of the people.) 

(4) They should be constructed so that the pit can easily be 
cleaned out. 

(5) The inlet should be so constructed as not easily to be choked 
by leaves or debris. 

(6) They must offer the least possible obstruction to traffic. 

(7) The pipe connecting the basin to the sewer should be easily 
freed of any obstruction. 

The bottom of the basins should be 6 or 8 feet below the street 
level; and the water level in them should be from 3 to 4 feet lower than 
the street surface, as a protection against freezing. 

The capacity and number of basins will depend upon the area of 
gurface which they drain, 






80 


HIGHWAY CONSTRUCTION 


In streets having level or light longitudinal grades, gullies may be 
formed along the line of the gutter at such intervals as may be found 
necessary. 

Catch-basins are usually placed at the curb line. In several cities, 
the basin is placed in the center of the street, and connects to 
inlets placed at the curb line. This reduces the cost of construction 
and cleaning, and removes from the sidewalk the dirty operations of 
cleaning the basins. 

Catch-basins and gully-pits require to be cleaned out at frequent 
intervals; otherwise the odor arising from the decomposing matter 
contained in them will be very offensive. No rule can be laid down 
for the intervals at which the cleaning should be done, but they must 
be cleaned often enough to prevent the matter in them from putrefying. 
There is no uniformity of practice observed by cities in this matter; in 
some, the cleaning is done but once a year; in others, after every rain¬ 
storm; in still others, at intervals of three or four months; while in a 
few cities the basins are cleaned out once a month. 

FOUNDATIONS 

The stability, permanence, and maintenance of any pavement 
depend upon its foundation. If the foundation is weak, the surface 
will soon settle unequally, forming depressions and ruts. With a good 
foundation, the condition of the surface will depend upon the material 
employed for the pavement and upon the manner of laying it. 

The essentials necessary to the forming of a good foundation are: 

(1) The entire removal of all vegetable, perishable, and yielding 
matter. It is of no use to lay good material on a bad substratum. 

(2) The drainage of the subsoil wherever necessary. A per¬ 
manent foundation can be secured only by keeping the subsoil dry; 
for, where water is allowed to pass into and through it, its weak spots 
will be quickly discovered and settlement will take place. 

(3) The thorough compacting of the natural soil by rolling with 
a roller of proper weight and shape until it forms a uniform and un¬ 
yielding surface. 

(4) The placing on the natural soil so compacted, a sufficient 
thickness of an impervious and incompressible material to cut off all 
communication between the soil and the bottom of the pavement. 

The character of the natural soil over which the roadway is to be 
built has an important bearing upon the kind of foundation and the 
manner of forming it; each class of soil will require its own special 




HIGHWAY CONSTRUCTION 


81 


treatment. Whatever its character, it must be brought to a dry and 
tolerably hard condition by draining and rolling. Sand and gravels 
which do not hold water, present no difficulty in securing a solid and 
secure foundation; clays and soils retentive of water are the most 
difficult. Clay should be excavated to a depth of at least 18 inches 
below the surface of the finished covering; and the space so excavated 
should be filled in with sand, furnace slag, ashes, coal dust, oyster 
shells, broken brick, or other materials which are not excessively absorb¬ 
ent of water. A clay soil or one retaining water may be cheaply and 
effectually improved by laying cross-drains with open joints at inter¬ 
vals of 50 or 100 feet. These drains should be not less than 18 inches 
below the surface, and the trenches filled with gravel. They should 
be 4 inches in internal diameter, and should empty into longitudinal 
drains. 

Sand and planks, gravel, and broken stone have been successively 
used to form the foundation for pavements; but, although eminently 
useful materials, their application to this purpose has always been a 
failure. Being inherently weak and possessing no cohesion, the main 
reliance for both strength and wear must be placed upon the surface- 
covering. This covering—usually (except in case of sheet asphalt) 
composed of small units, with joints between them varying from one- 
half an inch to one and a-half inches—possesses no elements of cohe¬ 
sion; and under the blows and vibrations of traffic the independent 
units or blocks will settle and be jarred loose. On account of their 
porous nature, the subsoil quickly becomes saturated with urine and 
surface waters, which percolate through the joints; winter frosts up¬ 
heave them; and the surface of the street becomes blistered and broken 
up in dozens of places. 

Concrete. As a foundation for all classes of pavement (broken 
stone excepted), hydraulic-cement concrete is superior to any other. 
When properly constituted and laid, it becomes a solid, coherent mass 
capable of bearing great weight without crushing. If it fail at all, it 
must fail altogether. The concrete foundation is the most costly, but this 
is balanced by its permanence and by the saving in the cost of repairs to 
the pavement which it supports. It admits of access to subterranean 
pipes with less injury to the neighboring pavement than any other, for 
the concrete may be broken through at any point without unsettling 
the foundation for a considerable distance around it, as is the case with 






82 


HIGHWAY CONSTRUCTION 


sand or other incoherent material; and when the concrete is replaced 
and set, the covering may be reset at its proper level, without the un¬ 
certain allowance for settlement which is necessary in other cases. 

Thickness of Concrete. The thickness of the concrete bed must 
be proportioned by the engineer; it should be sufficient to provide 
against breaking under transverse strain caused by the settlement of 
the subsoil. On a well-drained soil, six inches will be found sufficient; 
but in moist and clayey soils, twelve inches will not be excessive. On 
such soils a layer of sand or gravel, spread and compacted before pla¬ 
cing the concrete, will be found very beneficial. 

The proportions of the ingredients for concrete used for pavement 
foundations are usually: 

1 part Portland cement 

3 parts Sand 

7 parts Broken Stone. 

Or, 

1 part Natural Hydraulic Cement 

2 parts Sand 

5 parts Broken Stone. 

The cjuestion is sometimes raised as to whether Natural or Port¬ 
land cement should be used. Natural cement is more extensively 
employed on account of its being cheaper in price than Portland. 
There is no advantage gained in using Portland cement. Concrete 
should not be laid when the temperature falls below 32° F. 

The concrete foundation, after completion, should be allowed to 
remain several days before the pavement is placed upon it, in order 
that the mortar may become entirely set. During setting, the con¬ 
crete should be protected from the drying action of the sun and 
wind, and should be kept damp to prevent the formation of drying 
cracks 

STONE BLOCK PAVEMENTS 

Stone blocks are commonly employed for pavements where traffic 
is heavy. The material of which the blocks are made should possess 
sufficient hardness to resist the abrasive action of traffic, and sufficient 
toughness to prevent them from being broken by the impact of loaded 
wheels. The hardest stones will not necessarily give the best re¬ 
sults in the pavement, since a very hard stone usually wears smooth 
gnd becomes slippery. The edges of the block chip off, and the 






HIGHWAY CONSTRUCTION 


83 


upper face becomes rounded, thus making the pavement very 
rough. 

The stone is sometimes tested to determine its strength, resistance 
to abrasion, etc.; but, as the conditions of use are quite different from 
those under which it may be tested, such tests are seldom satisfactory. 
However, examination of a stone as to its structure, the closeness of its 
grain, its homogeneity, porosity, etc., may assist in forming an idea of 
its value for use in a pavement. A low degree of permeability usually 
indicates that the material will not be greatly affected by frost. 

Materials.—Granite. Granite is more extensively employed for 
stone block paving than any other variety of stone; and because of this 
fact, the term “granite paving” is generally used as being synonymous 
with stone block paving. The granite employed should be of a tough, 
homogeneous nature. The hard, quartz granites are usually brittle, 
and do not wear well under the blows of horses’ feet or the impact of 
vehicles; granite containing a high percentage of feldspar will be inju¬ 
riously affected by atmospheric changes; and granite in which mica 
predominates will wear rapidly on account of its laminated structure. 
Granite possesses the very important property of splitting in three 
planes at right angles to one another, so that paving blocks may readily 
be formed with nearly plane faces and square corners. This property 
is called the rift or cleavage. 

Sandstones of a close-grained, compact nature often give very 
satisfactory results under heavy traffic. They are less hard than 
granite, and wear more rapidly, but do not become smooth and slip¬ 
pery. Sandstones are generally known in the market by the name 
of the quarry or place where produced as “Medina,” “Berea,” 
etc. 

Trap rock, while answering well the requirements as to durability 
and resistance to wear, is objectionable on account of its tendency to 
wear smooth and become slippery; it is also difficult to break into 
regular shapes. 

Limestone has not usually been successful in use for the construc¬ 
tion of block pavements, on account of its lack of durability against 
atmospheric influences. The action of frost commonly splits the 
blocks; and traffic shivers them, owing to the lamination being 
vertical, 






84 


HIGHWAY CONSTRUCTION 


TABLE 12. 

Specific Gravity, Weight, Resistance to Crushing, and 
Absorption Power of Stones. 


Material 

Specific 

Gravity 

Weight 
P ounds 
per cu. ft. 

| RESISTANCE 

to Crushing 
P ounds 
per sq. in. 

PERCENTAGE 

of Water 
Absorbed 

Granite — 





Maximum. 

2.80 

176 

35,000 

0.155 

Minimum. 

2.60 

163 

12,000 

0.066 

Trap — 





Maximum. 

3.03 

178 

24,000 

0.019 

Minimum . 

2.86 

189 

19,000 

0.000 

Sandstone — 





Maximum. 

2.75 

170 

18.000 

5.480 

Minimum . 

2.23 

137 

5,000 

0.410 

Limestone — 





Maximum ...... 

2.75 

175 

20,000 

5.000 

Minimum. 

1.90 

118 

7,000 

0.200 

Brick Paving — 





Maximum.. 

1.95 


20.000 


Minimum 

2.55 


10,000 



Cobblestone Pavement. Cobblestones bedded in sand possess 
the merit of cheapness, and afford an excellent foothold for horses; 
but the roughness of such pavements requires the expenditure of a 
large amount of tractive energy to move a load over them. Aside from 
this, cobblestones are entirely wanting in the essential requisites of a 
good pavement. The stones being of irregular size, it is almost impos¬ 
sible to form a bond or to hold them in place. Under the action of the 
traffic and frost, the roadway soon becomes a mass of loose stones. 
Moreover, cobblestone pavements are difficult to keep clean, and very 
unpleasant to travel over. 

Belgian Block Pavement. Cobblestones were displaced by pave¬ 
ments formed of small cubical blocks of stone. This type of 
pavement was first laid in Brussels, thence imported to Paris, and from 
there taken to the United States, where it has been widely known as 
the “Belgian block” pavement. It has been largely used in New YY>rk 
City, Brooklyn, and neighboring towns, the material being trap-rock 
obtained from the Palisades on the Hudson River. 

The stones, being of regular shape, remain in place better than 
cobblestones; but the cubical form (usually five inches in each dimen¬ 
sion) is a mistake. The foothold is bad; the stones wear round; and 
the number of joints is so great that ruts and hollows are quickly 
formed. This pavement offers less resistance to traction than cobble¬ 
stones, but it is almost equally rough and noisy. 

Granite Block Pavement. The Belgian block has been gradually 

































HIGHWAY CONSTRUCTION 


85 


displaced by the introduction of rectangular blocks of granite. Blocks 
of comparatively large dimensions were at first employed. They were 
from 6 to 8 inches in width on the surface, from 10 to 20 inches in 
length, with a depth of 9 inches. They were merely placed in rows 
on the subsoil, perfunctorily rammed, the joints filled with sand, and 
the street thrown open to traffic. The unequal settlement of the 
blocks, the insufficiency of the foothold, and the difficulty of cleansing 
the street, led to the gradual development of the latest type of stone- 
block pavement, which consists of narrow, rectangular blocks of 
granite, properly proportioned, laid on an unyielding and impervious 
foundation, with the joints between the blocks filled with an imper¬ 
meable cement. 

Experience has proved beyond doubt that this latter type of 
pavement is the most enduring ar d economical for roadways subjected 
to heavy and constant traffic. Its advantages are many, while its 
defects are few. 

Advantages. 

(1) Adaptability to all grades. 

(2) Suits all classes of traffic. 

(3) Exceedingly durable. 

(4) Foothold, fair. 

(5) Requires but little repair. 

(6) Yields but little dust or mud. 

(7) Facility for cleansing, fair. 

Defects. 

(1) Under certain conditions of the atmosphere, the surface of 
the pavement becomes greasy and slippery. 

(2) The incessant din and clatter occasioned by the movement 
of traffic is an intolerable nuisance; it is claimed by many physicians 
that the noise injuriously affects the nerves and health of persons who 
are obliged to live or do business in the vicinity of streets so paved. 

(3) Horses constantly employed upon it soon suffer from the 
continual jarring produced in their legs and hoofs, and quickly wear 
out. 

(4) The discomfort of persons riding over the pavement is very • 
great, because of the continual jolting to which they are subjected. 

(5) If stones of an unsuitable quality are used—for example, 




86 


HIGHWAY CONSTRUCTION 


those that polish—the surface quickly becomes slippery and exceed¬ 
ingly unsafe for travel. 

Size and Shape of Blocks. The proper size of blocks for paving 
purposes has been a subject of much discussion, and a great variety of 
forms and dimensions are to be found in all cities. 

For stability, a certain proportion must exist between the depth, 
the length, and the breadth. The depth must be such that when the 
wheel of a loaded vehicle passes over one edge of the upper surface 
of a block, the block will not tend to tip up. The resultant direction 
of the pressure of the load and adjoining blocks should always tend 
to depress the whole block vertically; where this does not happen, the 
maintenance of a uniform surface is impossible. To fulfil this require¬ 
ment, it is not necessary to make the block more than six inches deep. 

Width of Blocks. The maximum width of blocks is controlled 
by the size of horses’ hoofs. To afford good foothold to horses draw¬ 
ing heavy loads, it is necessary that the width of each block, measured 
along the street, shall be the least possible consistent with stability. 


Gutter formed of 3 rows of 
b/ocks,Se! /ongirudinalh 



If the width be great, a horse drawing a heavy load, attempting to find 
a joint, slips back, and requires an exceptionally wide joint to pull him 
up. It is therefore desirable that the width of a block shall not exceed 
3 inches; or that four blocks, taken at random and placed side by side, 
shall not measure more than 14 inches. 

Length of Blocks, The length, measured across the street; 
must be sufficient to break joints properly, for two or more joints in 
line lead to the formation of grooves. For this purpose the length 
of the block should be not less than 9 inches nor more than 12 inches. 

Form of Blocks. The blocks should be well squared, and must 
not taper in any direction; sides and ends should be free from irregular 
projections. Blocks that taper from the surface downwards (wedge- 
shaped) should not be permitted in the work; but if any are allowed, 
they should be set with the widest side down. 


































HIGHWAY CONSTRUCTION 


87 


Manner of Laying Blocks- The blocks should be laid in parallel 
courses, with their longest side at right angles to the axis of the street, 
and the longitudinal joints broken by a lap of at least two inches (see 
Figs. 54 and 55). The reason for this is to prevent the formation of 
longitudinal ruts, which would happen if the blocks were laid length¬ 
wise. Laying blocks obliquely and “herring-bone” fashion has been 



tried in several cities, with the idea that the wear and formation of ruts 
would be reduced by having the vehicle cross the blocks diagonally. 
The method has failed to give satisfactory results; the wear was ir¬ 
regular and the foothold defective; the difficulty of construction was 
increased by reason of labor required to form the triangular joints; and 
the method was wasteful of material. 



7- 1 - 7 

Fig. 56. 


The gutters should be formed by three or more courses of block, 
laid with their length parallel to the curb- 

At junctions or intersections of streets, the blocks should be laid 
diagonally from the center, as shown in Fig. 56. The reasons for 

























































































88 


HIGHWAY CONSTRUCTION 


this are: (1) To prevent the traffic crossing the intersection from 
following the longitudinal joints and thus forming depressions and 
ruts; (2) Laid in this manner, the blocks afford a more secure foot¬ 
hold for horses turning the corners. The ends of the diagonal blocks 
where they abut against the straight blocks, must be cut to the re¬ 
quired bevel. 

The blocks forming each course must be of the same depth, and 
no deviation greater than one-quarter of an inch should be permitted. 
The blocks should be assorted as they are delivered, and only those 
corresponding in depth and width should be used in the same course. 
The better method would be to gauge the blocks at the quarry. 
This would lessen the cost considerably; it would also avoid the in¬ 
convenience to the public due to the stopping of travel because of the 
rejection of defective material on the ground. This method woidd 
undoubtedly be preferable to the contractor, who would be saved the 
expense of handling unsatisfactory material; and it would also leave 
the inspectors free to pay more attention to the manner in which the 
work of paving is performed. 

The accurate gauging of the blocks is a matter of much impor¬ 
tance. If good work is to be executed, the blocks, when laid, must be 
in parallel and even courses; and if the blocks be not accurately gauged 
to one uniform size, the result will be a badly paved street, with the 
courses running unevenly. The cost of assorting blocks into lots of 
uniform width, after delivery on the street, is far in excess of any ad¬ 
ditional price which would have to be paid for accurate gauging at the. 
quarry. 

Foundation. The foundation of the blocks must be solid and 
unyielding. A bed of hydraulic-cement concrete is the most suitable, 
the thickness of which must be regulated according to the traffic; the 
thickness, however, should not be less than 4 inches, and need not be 
more than 9 inches. A thickness of 6 inches will sustain traffic of 600 
tons per foot of width. 

Cushion Coat. Between the surface of the concrete and the base 
of the blocks, there must be placed a cushion-coat formed of an incom¬ 
pressible but mobile material, the particles of which will readily adjust 
themselves to the irregularities of the bases of the blocks and transfer 
the pressure of the traffic uniformly to the concrete below. A layer 
of dry, clean sand 1 to 2 inches thick forms an excellent cushion-coat. 






HIGHWAY CONSTRUCTION 


89 


Its particles must he of such fineness as to pass through a No. <8 screen; 
if coarse and containing pebbles, they will not adapt themselves to the 
irregularities of the bases of the blocks; hence the blocks will be sup¬ 
ported at only a few points, and unequal settlement will take place when 
the pavement is subjected to the action of traffic. The sand must also 
be perfectly free from moisture, and artificial heat must be used to dry 
it if necessary. This requirement is an absolute necessity. There 
should be no moisture below the blocks when laid; nor should water 
be allowed to penetrate below the blocks; if such happens, the effect of 
frost will be to upheave the pavement and crack the concrete. 

Where the best is desired without regard to cost, a layer half an 
inch thick of asphaltic cement may be substituted for the sand, with 
superior and very satisfactory results. 

Laying Blocks. The blocks should be laid stone to stone, so that 
the joint may be of the least possible width; wide joints cause increased 
wear and noise, and do not increase the foothold. The courses should 
be commenced on each side and worked toward the middle; and the 
last stone should fit tightly. 

Ramming. After the blocks have been set, they should be well 
rammed down; and the stones which sink below the general level 
should be taken up and replaced with a deeper stone or brought to 
level by increasing the sand bedding. 

The practice of workmen is invariably to use the rammer so as to 
secure a fair surface. This is not the result intended to be secured, 
but to bring each block to an unyielding bearing. The result of such 
a surfacing process is to produce an unsightly and uneven roadway 
when the pressure of traffic is brought upon it. The rammer used 
should weigh not less than 50 pounds and have a diameter of not less 
than 3 inches. 

Joint Filling. All stone block pavements depend for their water¬ 
proof qualities upon the character of the joint filling. Joints filled 
with sand and gravel are of course pervious. A grout of lime or cement 
mortar does not make a permanently waterproof joint; it becomes 
disintegrated under the vibration of traffic. An impervious joint can 
be made only by employing a filling made from bituminous or asphaltic 
material; this renders the pavement more impervious to moisture, 
makes it less noisy, and adds considerably to its strength. 

Bituminous Cement for Joint Filling. The bituminous materials 


90 


HIGHWAY CONSTRUCTION 


employed are: (1) The tar produced in the manufacture of gas, 
which, when redistilled, is called distillate, and is numbered 1, 2, 3, 4, 
etc., according to its density; this material under the name of paving- 
pitch is extensively used, both alone and in combination with other 
bituminous substances; (2) Combinations of gas tar or coal tar with 
refined asphaltum; (3) Mixtures of refined asphaltum, creosote, and 
coal tar. 

The formula for the bituminous joint filling used in New York 


City, is: 

Refined Trinidad asphaltum. 20 parts. 

No. 4 coal-tar distillate. 100 parts. 

Residuum of petroleum. 3 parts. 


In Washington, D. C., coal tar distillate No. 6 is used alone. 

In Europe a bituminous cement much used is composed of coal- 
tar, asphaltum, gas tar, and creosote oil, in the proportion of 100 
pounds of asphaltum to 4 gallons of tar and 1 gallon of creosote. 
These proportions are varied somewhat, according to the quality of the 
asphaltum employed. The mixture is melted, and is boiled from 
one to two hours in a suitable boiler, being then poured into the joints 
in a boiling state. This mixture is impervious to moisture, and pos¬ 
sesses a degree of elasticity sufficient to prevent it from cracking. 

The mode of applying the bituminous cement is as follows: After 
the blocks are rammed, the joints are filled to a depth of about two 
inches with clean gravel heated to a temperature of about 250° F.; 
then the hot cement is poured in until it forms a layer of about one inch 
on top of the gravel; then more gravel is filled in to a depth of about 
two inches; then cement is poured in until it appears on top of the 
gravel, more gravelling next added until it reaches to within half an 
inch of the top of the blocks; this remaining half-inch is filled with 
cement, and then fine gravel or sand is sprinkled over the joints. 

In some cases the joints are first filled with heated gravel; the 
cement is poured in until the sand beneath and the gravel between 
the blocks will absorb no more, and the joints are filled flush with the 
top of the pavement. This method is open to objection; for, if the 
gravel is not sufficiently hot, the cement will be chilled and will not flow 
to the bottom of the joint, but, instead, will form a thin layer near the 
surface, which under the action of frost and the vibration of traffic, 
will be quickly cracked and broken up; the gravel will settle, and the 








HIGHWAY CONSTRUCTION 


91 


blocks will be jarred loose, the surface of the pavement becoming a 
series of ridges and hollows. 

The quantity of cement required per square yard of pavement will 
vary according to the shape of the blocks, the width of the joints, and 
the depth of the sand bed. With well-shaped blocks, close joints, and 
a half-inch sand bed, the quantity will vary from 3-V to 5 gallons; with 
ill-shaped blocks, wide joints, and a heavy sand bed, 10 to 12 gallons 


Fig. 57. 



would not be an excessive amount to use to secure the result obtained 
by employing well-shaped blocks and close joints. 

Stone Pavement on Steep Grades. Stone blocks may be em¬ 
ployed on all practicable grades; but on grades exceeding 10 per cent, 
cobblestones afford a better foothold than blocks. The cobblestones 
should be of uniform length, the length being at least twice the breadth 
—say stones 6 inches long and 2\ to 3 inches in diameter. These 
should be set on a concrete foundation, laid stone to stone, and the 



interstices filled with cement grout or bituminous cement; or a bitu¬ 
minous concrete foundation may be employed and the interstices be¬ 
tween the stones filled with asphaltic paving cement. Should stone 
blocks be preferred, they must be laid, when the grade exceeds 5 per 
cent, with a serrated surface, by either of the methods shown in Figs. 
57 and 58. The method shown in Fig. 57 consists in slightly tilting 
the blocks on their bed so as to form a series of ledges or steps, against 
which the horses’ feet being planted, a secure foothold is obtained. 
The method shown in Fig. 58 consists in placing between the rows of 













92 


HIGHWAY CONSTRUCTION 


stones a course of slate, or strips of creosoted wood, rather less than 
one inch in thickness and about an inch less in depth than the blocks; 
or the blocks may be spaced about one inch apart, and the joints filled 
with a grout composed of gravel and cement. The pebbles of the 
gravel should vary in size between one-quarter and three-quarters of 
an inch. 


BRICK PAVEMENTS 

Characteristics of Brick Suitable for Paving. These are: 

(1) Not to be acted upon by acids. 

(2) Not to absorb more than 1-600 of its weight of water in 
48 hours. 


(3) Not susceptible to polish. 

(4) Rough to the touch, resembling fine sandpaper. 

(5) To give a clear, ringing sound when struck together. 

(6) When broken, to show a compact, uniform, close-grained, 
structure, free from air-holes and pebbles. 

(7) Not to scale, spall, or chip when quickly struck on the edges. 

(8) Hard but not brittle. 

Tests of Paving Brick. To ascertain the quality of paving brick, 
they are generally subjected to four tests, namely: (1) Abrasion by 

impact (commonly called the “Rattler” test); (2) absorption; (3) 
transverse or cross-breaking; (4) crushing. With a view to securing 
uniformity in the methods of making the above tests, the National 
Brick Manufacturers’ Association has adopted and recommends the 
following: 

Rattler Test 

1. Dimensions of the Machine. The standard machine shall 
be 28 inches in diameter and 20 inches in length, measured inside the 
chamber. 

Other machines may be used, varying in diameter between 26 and 
30 inches, and in length between 18 and 24 inches; but if this is done, 
a record of it must be attached to the official report. Long rattlers 
may be cut up into sections of suitable length by the insertion of an 
iron diaphragm at the proper point. 

2 Construction of the Mach ine. The barrel shall be supported 
on trunnions at either end; in no case shall a shaft pass through the 
rattling chamber. The cross-section of the barrel shall be a regular 
polygon having 14 sides. The heads shall be composed of grav cast- 


HIGHWAY CONSTRUCTION 


93 


iron, not chilled or case-hardened. The staves shall preferably be 
composed of steel plates, since cast-iron peans and ultimately breaks 
under the wearing action on the inside. There shall be a space of one- 
fourth of an inch between the staves, for the escape of dust and small 
pieces of waste. Other machines may be used, having from twelve to 
sixteen staves; but if this is done, a record of it must be attached to 
the official report of the test. 

3. Composition of the Charge. All tests must be executed on 
charges containing but one make of brick or block at a time. The 
charge shall consist of 9 paving blocks or 12 paving bricks, together 
with 300 pounds of shot made of ordinary machinery cast-iron. This 
shot shall be of two sizes, as described below; and the shot charge shall 
be composed one-fourth (75 pounds) of the larger size, and three- 
fourths (225 pounds) of the smaller size. 

4. Size of the Shot. The larger size shall weigh about 7\ pounds 
and be about 24 inches square and 44 inches long, with slightly round¬ 
ed edges. The smaller size shall be cubes of 14 inches on a side, with 
rounded edges. The individual shot shall be replaced by new ones 
when they have lost one-tenth of their original weight. 

5. Revolutions of the Charge. The number of revolutions of a 
standard test shall be 1,800; and the speed of rotation shall not fall 
below 28 nor exceed 30 revolutions per minute. The belt-power shall 
be sufficient to rotate the rattler at the same speed, whether charged 
or empty. 

6. Condition of the Charge. The bricks composing a charge 
shall be thoroughly dried before making the test. 

7. Calculation of the Results. The loss shall be calculated in 
per cents of the weight of the dry brick composing the charge; and no 
result shall be considered as official unless it is the average of two 
distinct and complete tests made on separate charges of brick. 

Absorption Test 

1. The number of bricks for a standard test shall be five. 

2. The test must be conducted on rattled brick. If none such 
are available, t he whole brick must be broken in halves before treatment. 

3. Dry the bricks for 48 hours at a temperature ranging from 
230° to 250° F. before weighing for the official dry weight. 

4. Soak for 48 hours completely immersed in pure water. 



94 


HIGHWAY CONSTRUCTION 


5. After soaking, and before weighing, the bricks must be wiped 
dry from surplus water. 

6. The difference in the weight must be determined on scales 
sensitive to one gram. 

7. The increase in weight due to water absorbed shall be cal¬ 
culated in per cents of the initial dry weight. 

Cross=Breaking Test 

1. Support the brick on edge, or as laid in the pavement, on 
hardened steel knife-edges, rounded longitudinally to a radius of 
twelve inches and transversely to a radius of one-eighth inch, and 
bolted in position so as to secure a span of six inches. 

2. Apply the load to the middle of the top face through a hard¬ 
ened steel knife-edge, straight longitudinally and rounded transversely 
to a radius of one-sixteenth inch. 

3. Apply the load at a uniform rate of increase till fracture 
ensues. 

4. Compute the modulus of rupture by the formula 

,_3 w l 

' ~2 Jd 2 ’ 

in which / = modulus of rupture, in pounds per square inch; 
w = total breaking load, in pounds; 
l = length of span, in inches =6; 
b = breadth of brick, in inches* 
d = depth of brick, in inches. 

5. Samples for test must be free from all visible irregularities of 
surface or deformities of shape, and their upper and lower faces must 
be practically parallel. 

6. Not less than ten brick shall be broken, and the average of all 
shall be taken for a standard test. 

Crushing Test 

1. The crushing test should be made on half-bricks, loaded 
edgewise, or as they are laid in the street. If the machine used is 
unable to crush a full half-brick, the area may be reduced bv chipping 
off, keeping the form of the piece to be tested as nearly prismatic as 
possible. A machine of at least 100,000 pounds’ capacity should be 
used; and the specimen should not be reduced below four square 
inches of area in cross-section at right angles to direction of load. 

2. The upper and lower surfaces should preferably be ground to 



HIGHWAY CONSTRUCTION 


95 


true and parallel planes. If this is not done, they should be bedded, 
while in the testing machine, in plaster of Paris, which should be 
allowed to harden ten minutes under weight of the crushing planes 
only, before the load is applied. 

3. The load should be applied at a uniform rate of increase to 
the point of rupture. 

4. Not less than an average obtained from five tests on five 
• different bricks shall constitute a standard test. 

Properties of Paving Bricks. Paving bricks range in weight 
from 5J to 7^ pounds; in specific gravity, from 1.91 to 2.70; in resist¬ 
ance to crushing, from 7,000 to 18,000 pounds per square inch; in 
resistance to cross-breaking, R = 1,400 to 2,000 pounds; in absorption, 
from 0.15 to 3 per cent in 24 hours. The dimensions vary according to 
locality and the requirements of the specifications. The “standard” 
bricks are 21X4X8 inches, requiring 58 bricks to the square yard, 
and weighing 7 pounds each;“ repressed “, X 4 X8 J inches, requir¬ 
ing 61 to the square yard, and weighing 6J pounds each; “Metropoli¬ 
tan”, 3X4X9 inches, requiring 45 to the square yard, and weighing 
9^ pounds each. 

Advantages of Brick Pavements. These may be stated as follows: 

(1) Ease of traction. 

(2) Good foothold for horses. 

(3) Not disagreeably noisy. 

(4) Yields but little dust and mud. 

(5) Adapted to all grades. 

(6) Easily repaired. 

(7) Easily cleaned. 

(8) But slightly absorbent. 

(9) Pleasing to the eye. 

(10) Expeditiously laid. 

(11) Durable under moderate traffic. 

Defects of Brick Pavements. The principal defects of brick 
pavements arise from lack of uniformity in the quality of the bricks, 
and from the liability of incorporating in the pavement bricks of too 
soft or porous a structure, which crumbles under the action of traffic 
or frost. 

Foundation. A brick pavement should have a firm foundation. 
As the surface is made up of small, independent blocks, each one must 




96 


HIGHWAY CONSTRUCTION 


be adequately supported, or the load coining upon it may force it 
downwards and cause unevenness, a condition which conduces to the 
rapid destruction of the pavement. Several forms of foundation have 
been used—such as gravel, plank, sand, broken stone, and concrete. 
The last mentioned is doubtless the best. 

Sand Cushion. The sand cushion is a layer of sand placed on 
top of the concrete to form a bed for the brick. Practice regarding 
the depth of this layer of sand varies considerably. In some cases it 
is only half an inch deep, varying from this up to three inches. The 
sand cushion is very desirable, as it not only forms a perfectly true and 
even surface upon which to place brick, but also makes the pavement 
less hard and rigid than would be the case were the brick laid directly 
on the concrete. 

The sand is spread evenly, sprinkled with water, smoothed, and 
brought to the proper contour by screeds or wooden templets, properly 
trussed, mounted on wheels or shoes which bear upon the upper sur¬ 
face of the curb. Moving the templet forward levels and forms the 
sand to a uniform surface and proper shape. 

The sand used for the cushion-coat should be clean and free from 
loam, moderately coarse, and free from pebbles exceeding one-quarter 
inch in size. 

Manner of Laying. The bricks should be laid on edge, as closely 

and compactly as possible, in straight courses across the street, with 

the length of the bricks at right angles to the axis of the street. Joints 

should be broken by at least 3 inches. None but whole bricks should 

•/ 

be used, except in starting a course or making a closure. To provide 
for the expansion of the pavement, both longitudinal and transverse 
expansion-joints are used, the former being made by placing a board 
templet seven-eighths of an inch thick against the curb and abutting 
the brick thereto. The transverse joints are formed at intervals 
varying between 25 and 50 feet, by placing a templet or building-lath 
three-eighths of an inch thick between two or three rows of brick. 
After the bricks are rammed and ready for grouting, these templets are 
removed, and the spaces so left are filled with coal-tar pitch or asphal¬ 
tic paving cement. The amount of pitch or cement required will vary 
between one and one and a-half pounds per square yard of pavement, 
depending upon the width of the joints. After 25 or 30 feet of the 
pavement is laid, every part of it should be rammed with a rammer 





HIGHWAY CONSTRUCTION 


97 


weighing not less than 50 pounds; and the bricks which sink below the 
general level should be removed, sufficient sand being added to raise 
the brick to the required level. After all objectionable brick have 
been removed, the surface should be swept clean, then rolled with a 
steam roller weighing from 3 to 6 tons. The object of rolling is to 
bring the bricks to an unyielding bearing with a plane surface; if this 
is not done, the pavement will be rough and noisy and will lack dura¬ 



bility. The rolling should be first executed longitudinally, beginning 
at the crown and working toward the gutter, taking care that each 
return trip of the roller covers exactly the same area as the preceding 
trip, so that the second passage may neutralize any careening of the 
brick due to the first passage. 

The manner of laying brick at street intersections is shown in 


Fig. 59. 







































98 


HIGHWAY CONSTRUCTION 


Joint Filling. The character of the material used in filling the 
joints between the brick has considerable influence on the success and 
durability of the pavement. Various materials have been used—such 
as sand, coal-tar pitch, asphalt, mixtures of coal-tar and asphalt, and 
Portland cement, besides various patented fillers, as “Murphy’s 
grout”, which is made from ground slag and cement. Each material 
has its advocates, and there is much difference of opinion as to which 
gives the best residts. 

The best results seem to be obtained by using a high grade of 
Portland cement containing the smallest amount of lime in its composi¬ 
tion, the presence of the lime increasing the tendency of the filler to 
swell through absorption of moisture, causing the pavement to rise 
or to be lifted away from its foundation, and thus producing the roaring 
or rumbling noise so frequently complained of. 

The Portland cement grout, when uniformly mixed and carefully 
placed, resists the impact of traffic and wears well with brick. When a 
failure occurs, repairs can be made quickly; and, if made early, the 
pavement will be restored to a good condition. If, however, repairs 
are neglected, the brick soon loosens and the pavement fails. 

The office of a filler is to prevent water from reaching the founda¬ 
tion, and to protect the edges of the brick from spalling under traffic. 
In order to meet both of these requirements, every joint must be filled 
to the top, and must remain so, wearing down with the brick. Sand 
does not meet these requirements. Although at first making a good 
filler, being inexpensive and reducing the liability of the pavement to 
be noisy, it soon washes out, leaving the edges of the brick unprotected 
and consequently liable to be chipped. Coal-tar and the mixtures of 
coal-tar and asphalt have an advantage in rendering a pavement less 
noisy and in cementing together any breaks that may occur through 
upheavals from frost or other causes; but, unless made very hard, they 
have the disadvantage of becoming soft in hot weather and flowing 
to the gutters and low places in the pavement, there forming a black 
and unsightly scale and leaving the high parts unprotected. The 
joints, thus deprived of their filling, become receptacles for water, mud, 
and ice in turn; and the edges of the brick are quickly broken down. 
Some of these mixtures become so brittle in winter that they crack 
and fly out of the joints under the action of traffic. 

The Portland cement filler is prepared by mixing two parts of 

», «•* 4 

! <r. • 9 






HIGHWAY CONSTRUCTION 


99 


cement and one part of fine sand with sufficient water to make a thin 
grout. The most convenient arrangement for preparing and dis¬ 
tributing the grout is a water-tight wooden box carried on four wooden 
wheels about 12 inches in diameter. The box may be about 4 feet 
wide, 7 feet long, and 12 inches deep, furnished with a gate about 8 
inches wide, in the rear end. The box should be mounted on the 
wheels with an inclination, so that the rear end is about 4 inches lower 
than the front end. 

The operation of placing the filler is as follows: The cement and 
sand are placed in the box, and sufficient water is added to make a 
thin grout. The box is located about 12 feet from the gutter, the end 
gate opened, and about 2 cubic feet of the‘grout allowed to flow out 
and run over the top of the brick (care being taken to stir the grout 
while it is being discharged). If the brick are very dry, the entire 
surface of the pavement should be thoroughly wet with a hose before 
applying the grout ; if not, absorption of the water from the grout by 
the bricks will prevent adhesion between the bricks and the cement 
grout. The grout is swept into the joints by ordinary bass brooms. 
After about 100 feet in length of the pavement has been covered the 
box is returned to the starting-point, and the operation is repeated 
with a grout somewhat thicker than the first. If this second applica¬ 
tion is not sufficient to fill the joints, the operation is repeated as often 
as may be necessary to fill them. If the grout has been made too thin, 
or the grade of the street is so great that the grout will not remain long 
enough in place to set, dry cement may be sprinkled over the joints and 
swept in. After the joints are completely filled and inspected, allowing 
three or four hours to intervene, the completed pavement should be 
covered with sand to a depth of about half an inch, and the roadway 
barricaded, and no traffic allowed on it for at least ten days. 

The object of covering the pavement with sand is to prevent the 
grout from drying or settling too rapidly; hence, in dry and windy 
weather, it should be sprinkled from time to time. If coarse sand is 
employed in the grout, it will separate from the cement during the 
operation of filling the joints, with the result that many joints will be 
filled with sand and very little cement, while others will be filled with 
cement and little or no sand; thus there will be many spots in the pave¬ 
ment m which no bond is foimed between the bricks, and under the 
action of traffic these portions will quickly become defective. 


LOFC 





100 


HIGHWAY CONSTRUCTION 


The coal-tar filler is best applied by pouring the material from 
buckets, and brooming it into the joints with wire brooms. In order to 
fill the joints effectually, it must be used only when very hot. To 
secure this condition, a heating tank on wheels is necessary. It should 
have a capacity of at least five barrels, and be kept at a uniform tem¬ 
perature all day. One man is necessary to feed the fire and draw the 
material into the buckets; another, to carry the buckets from the heat- 
ing-tank to a third, who pours the material over the street. The latter 
sta:ts to pour in the center of the street, working backward toward the 
curb, and pouring a strip about two feet in width. A fourth man, 
with a wire broom, follows immediately after him, sweeping the sur¬ 
plus material toward the pourer and in the direction of the curb. This 
method leaves the entire surface of the pavement covered with a thin 
coating of pitch, which should immediately be covered with a light 
coating of sand; the sand becomes imbedded in the pitch. Under the 
action of traffic, this thin coating is cpiickly worn away, leaving the 
surface of the bricks clean and smooth. 

Tools Employed in Construction of Block Pavements. The 
principal tools required in constructing block pavements comprise 
hammers and rammers of varying sizes and shapes, depending on the 
material and size of the blocks to be laid; also crowbars, sand screens, 
and rattan and wire brooms. Cobblestones, square blocks, and brick 
require different types of both hammers and rammers for adjusting 
them to place and forcing them to their seat. A cobblestone rammer, 
for example, is usually made of wood (generally locust) in the shape of 
a long truncated cone, banded with iron at top and bottom, weighing 
about 40 pounds, and having two handles, one at the top and another 
on one side. A Belgian block rammer is slightly heavier, consisting 
of an upper part of wood set in a steel base; while a rammer for granite 
blocks is still heavier, comprising an iron base with cast-steel face, into 
which is set a locust plug with hickory handles. For laving brick, a 
wooden rammer shod with cast iron or steel and weighing about 27 
pounds is used. A light rammer of about 20 pounds’ weight, consist¬ 
ing of a metallic base attached to a long, slim wooden handle, is used 
for miscellaneous work, such as tamping in trenches, next to curbs, etc. 

Concrete=Mixing Machine. Where large quantities of concrete 
are required, as in the foundations of improved pavements, concrete 
can be prepared more expeditiously and economically by the use of 




HIGHWAY CONSTRUCTION 


101 


mechanical mixers, and the ingredients will be more thoroughly mixed, 
than by hand. 'Thorough incorporation of the ingredients is an essen¬ 
tial element in the quality of a concrete. When mixed by hand, how¬ 
ever, the incorporation is rarely complete, because it depends upon the 
proper manipulation of the hoe and shovel. The manipulation, 
although extremely simple, is rarely performed by the ordinary laborer 
unless he is constantly watched by the overseer. 

Several varieties of concrete-mixing machines are in the market. 
A convenient portable type is illustrated in Fig. 60. The capacity of 




Fig. 60. Concrete Mixing Machine. 




■pal 

!ujp 



WM\ 

sU 

£8 


lijly-i 

1 



the mixers ranges from five to twenty cubic yards per hour, depending 
upon size, regularity with which the materials are supplied, speed, etc. 

Gravel Heaters. Fig. 61 illustrates a device commonly employed 
for heating the gravel used for joint filling in stone-block pavements. 
These heaters are made in various sizes, a common size being 9 feet 
long, 5 feet wide, and 3 feet 9 inches high. 

Melting Furnaces, for heating the pitch or tar for joint filling, are 
illustrated by Fig. 62. Various sizes are on the market. 

WOOD PAVEMENTS 

Wood pavements are formed of either rectangular or cylindrical 
blocks of wood. The rectangular blocks are generally 3 inches wide, 


















102 


HIGHWAY CONSTRUCTION 


0 inches long, and 6 inches deep; the round blocks are commonly 0 
inches in diameter and 6 inches long. 

The kinds of wood most commonly used are cedar, cypress, juni¬ 
per, yellow pine, and mesquite; and recently jarrah from Australia, 
and pyingado from India, have been used. 

The wood is used in its natural condition, or impregnated with 
creosote or other chemical preservative. 

The blocks of wood are laid either on the natural soil, on a bed 
of sand and gravel, on a layer of broken stone, on a layer of concrete, 




or, sometimes, on a double layer of plank. The joints are filled either 
with sand, paving-pitch, or Portland-cement grout. 

Advantages. The advantages of wood pavement may be stated 
as follows: 

(1) It affords good foothold for horses. 

(2) It offers less resistance to traction than stone, and slightly 
more than asphalt. 

(3) It suits all classes of traffic. 

(4) It may be used on grades up to five per cent. 

(5) It is moderately durable. 

(6) It yields no mud when laid upon an impervious foundation. 

(7) It yields but little dust. 











































HIGHWAY CONSTRUCTION 


103 


(8) It is moderate in first cost. 

(0) It; is not disagreeably noisy. 

Defects. The principal objections to wood pavement are: 

(1) It is difficult to cleanse. 

(2) Under certain conditions of the atmosphere it becomes 
greasy and very unsafe for horses. 

(3) It is not easy to open for the purpose of gaining access to 
underground pipes, it being necessary to remove rather a large surface 
for this purpose, which has to be left a little time after being repaired 
before traffic is again allowed upon it. 

(4) It is absorbent of moisture. 

(5) It is claimed by many that wood pavements are unhealthy. 

Quality of Wood. The question as to which of the various kinds 

of wood available is the most durable and economical, has not 
been satisfactorily determined. Many varieties have been tried. In 
England, preference is given to Baltic fir, yellow pine, and Swedish 
yellow deal. In the United States the variety most used (on account 
of its abundance and cheapness) is cedar; but yellow pine, tamarack, 
and mesquite have also been used to a limited extent, and cypress and 
juniper are being largely used in some of the Southern States. 

Hardwoods, such as oak, etc., do not make the best pavements, as 
such w r oods become slippery. The softer, close-grained woods, such 
as cedar and pine, wear better and give good foothold. 

The wood employed should be sound and seasoned, free from sap, 
shakes, and knots. Defective blocks laid in the pavement will quickly 
cause holes in the surface, and the adjoining blocks will suffer under 
w r ear, the whole surface becoming bumpy. 

Chemical Treatment of Wood. The great enemy of all wood 
pavements is decay, induced by the action of the air and water. Wood 
is porous, absorbs moisture, and thus hastens its own destruction. 
Many processes have been invented to overcome this defect. The 
most popular processes at present are creosoting and modifications of 
the same, known as the “creo-resinate” and “kreodine” processes. 
These consist of creosote mixed with various chemicals which are 
supposed to add to the preserving qualities of the creosote. 

Creosoting. This process consists in impregnating the wood with 
the oil of tar, called creosote, from which the ammonia has been ex¬ 
pelled, the effect being to coagulate the albumen and thereby prevent 




104 


HIGHWAY CONSTRUCTION 


its decomposition, also to fill the pores of the wood with a bituminous* 
substance which excludes both air and moisture, and which is noxious 
to the lower forms of animal and vegetable life. In adopting this pro¬ 
cess, all moisture should be dried out of the pores of the timber. The 
softer woods, while warm from the drying-house, may be immersed at 
once in an open tank containing hot creosote oil, when they will absorb 
about 8 or 9 pounds per cubic foot. For hardwoods, and woods which 
are required to absorb more than 8 or 9 pounds of creosote per cubic 
foot, the timber should be placed in an iron cylinder with closed ends, 
and the creosote, which should be heated to a temperature of about 
120 p F., forced in with a pressure of 170 pounds to the square inch. 
The heat must be kept up until the process is complete, to prevent the 
creosote from crystallizing in the pores of the wood. By this means 
the softer woods will easily absorb from 10 to 12 pounds of oil per cubic 
foot. 

The most effective method, however, is to exhaust the air from tht 
cylinder after the timber is inserted; then to allow the oil to flow in; and 
when the cylinder is full, to use a force pump with a pressure of 150 to 
200 pounds per square inch, until the wood has absorbed the requisite 
quantity of oil, as indicated by a gauge, which should be fitted to the 
reservoir tank. 

The oil is usually heated by coils of pipe placed in the reservoir, 
through which a current of steam is passed. 

The cpiantity of creosote oil recommended to be forced into the 
wood is from 8 to 12 pounds per cubic foot. Into oak and other hard 
woods it is difficult to force, even with the greatest pressure, more than 
2 or 3 pounds of oil. 

The advantages of this process are: The chemical constituents of 
the oil preserve the fibers of the wood by coagulating the albumen of 
the sap; the fatty matters act mechanically by filling the pores and thus 
exclude water; while the carbolic acid contained in the oil is a powerful 
disinfectant. 

The life of the wood is extended by any of the above processes, by 
preserving it from decay; but such processes have little or no effect on 
the wear of the blocks under traffic. 

The process of dipping the blocks in coal tar or creosote oil is 
injurious. Besides affording a cover for the use of defective or sappv 
wood, it hastens decay, especially of green wood; it closes up the ex- 



HIGHWAY CONSTRUCTION 


105 


terior of the cells of the wood so that moisture cannot escape, thus 
causing fermentation to take place in the interior of the block, which 
quickly destroys the strength of the fibers and reduces them to punk. 

Expansion of Blocks. Wood blocks expand on exposure to 
moisture; and, when they are laid end to end across the street, the 
curbstones are liable to be displaced, or the courses of the blocks will 
be bent into reserve curves. To avoid this, the joints of the courses 
near the curb may be left open until expansion has ceased, the space 
being temporarily filled with sand. The rate of expansion is about 
1 inch in 8 feet, but varies for different woods. The time required for 
the wood to become fully expanded varies from 12 to 18 months. By 
employing blocks impregnated with the oil of creosote, this trouble will 
be avoided. Blocks so treated do not contract or expand to any appre¬ 
ciable extent. 

The comparative expansion of creosoted and plain wood blocks 
after immersion in water for forty-eight hours, in percentage on orig¬ 
inal dimensions, was: 


Expansion of Wood Paving Blocks 


Dimension 

Creosoted 

Plain 

On length of block.. 

.099 

.6 

On width “ “ . 

.57 

.83 

On depth “ “ . 

.15 

.31 





Manner of Laying. The blocks are set with the fiber vertical, 
- and the long dimension crosswise of the street, the longitudinal joints 
being broken by a lap of at least one-third the length of the block; the 



blocks should be laid so as to have the least possible width of joint. 
Wide joints hasten the destruction of the wood by permitting the fibers 
to wear under traffic, which also causes the surface of the pavement 





































106 


HIGHWAY CONSTRUCTION 


to wear in small ridges. The most recent practice for laying blocks 
on 3 per cent grades, has been to remove from the top of one side of 
each block a strip J inch thick and 1 \ inches deep, extending the length 
of the block. When the blocks are laid and driven closely together, 
there is a quarter-inch opening or joint extending clear across the street 
in each course. These joints are filled with Portland cement grout. 
Fig. 63 shows a section of pavement having this form of joint. 

Filling for Joints. The best materials for filling the joints are 
bitumen for the lower two or three inches, and hydraulic cement grout 
for the remainder of the depth. The cement grout protects the pitch 
from the action of the sun, and does not wear down very much below 
the surface of the wood. 

ASPHALT PAVEMENTS. 

Asphaltic Paving Materials. All asphaltic or bituminous pave¬ 
ments are composed of two essential parts—namely, the cementing 
material (matrix) and the resisting material (aggregate). Each has a 
distinct function to perform; the first furnishes and preserves the co¬ 
herency of the mass; the second resists the wear of traffic. 

Two classes of asphaltic paving compounds are in use,—namely, 
natural and artificial. The “natural” variety is composed of either 
limestone or sandstone naturally cemented with bitumen. To this 
class belong the bituminous limestones of Europe, Texas, Utah, etc., 
and the bituminous sandstones of California, Kentucky, Texas, Indian 
Territory, etc. The “artificial” consists of mixtures of asphaltic 
cement with sand and stone dust. To this class belong the pavements 
made from Trinidad, Bermudez, Cuban, and similar asphaltums. 
For the artificial variety, most hard bitumens are, when properly 
prepared, equally suitable. For the aggregate, the most suitable mate¬ 
rials are stone-dust from the harder rocks, such as granite, trap, etc., 
and sharp angular sand. These materials should be entirely free from 
loam and vegetable impurities. The strength and enduring qualities 
of the mixture will depend upon the quality, strength, and proportion 
of each ingredient, as well as upon the cohesion of the matrix and its 
adhesion to the aggregate. 

Bituminous limestone consists of carbonate of lime naturally 
cemented with bitumen in proportions varying from 80 to 93 per cent 
of carbonate of lime and from 7 to 20 per cent of bitumen. Its color, 
when freshly broken, is a dark (almost black) chocolate brown, the 




HIGHWAY CONSTRUCTION 


107 


darker color being due to a large percentage of bitumen. At a tem¬ 
perature of from 55° to 70° F., the material is hard and sonorous, and 
breaks easily with an irregular fracture; at temperatures between 70° 
and 140° F. it softens, passing with the rise in temperature through 
various degrees of plasticity, until, at between 140° and 160° F., it 
begins to crumble; at 212° it commences to melt; and at 280° F. it is 
completely disintegrated. Its specific gravity is about 2.235. 

Bituminous limestone is the material employed for paving pur¬ 
poses throughout Europe. It is obtained principally from deposits 
at Val-de-Travers, canton of Neufchatel, Switzerland; at Seysell, in 
the Department of Ain, France; at Ragusa, Sicily; at Dimmer, near 
Hanover; and at Vorwohle, Germany. 

Bituminous limestone is found in several parts of the United 
States. Two of these deposits are at present being worked—one in 
Texas, the material from which is called “lithocarbon”; and one on the 
Wasatch Indian Reservation. These deposits contain from 10 to 30 
per cent of bitumen. 

The bituminous limestones which contain about 10 per cent of 
bitumen are used for paving in their natural condition, being simply 
reduced to powder, heated until thoroughly softened, then spread while 
hot upon the foundation, and tamped and rammed until compacted. 

Bituminous sandstones are composed of sandstone rock impreg¬ 
nated with bitumen in amounts varying from a trace to 70 per cent. 
They are found in both Europe and America. In Europe, they are 
chiefly used for the production of pure bitumen, which is extracted by 
boiling or macerating them with water. In the United States, exten- 
sive deposits are found in the Western States; and since 1880 they have 
been gradually coming into use as a paving material, so that now up¬ 
wards of 150 miles of streets in Western cities are paved with them. 
They are prepared for use as paving material by crushing to powder, 
which is heated to about 250° F. or until it becomes plastic, then spread 
upon the street and compressed by rolling; sometimes sand or gravel 
is added, and it is stated that a mixture of about 80 per cent of gravel 
makes a durable pavement. 

Trinidad Asphaltum. The deposits of asphaltum in the island 
of Trinidad, W. I., have been the main source of supply for the asphal¬ 
tum used in street paving in the United States. Three kinds are found 
there, which have been named, according to the source, lake-pitch , 




108 


HIGHWAY CONSTRUCTION 


land or overflow 'pitch, and iron pitch. The first and most valuable 
kind is obtained from the so-called Pitch Lake. 

The term land or overflow pitch is applied to the deposits of 
asphaltum found outside the lake. These deposits form extensive 
beds of variable thickness, and are covered with from a few to several 
feet of earth; they are considered by some authorities to be formed from 
pitch which has overflowed from the lake; by others to be of entirely 
different origin. The name cheese pitch is given to such portions of the 
land pitch as more nearly resemble that obtained from the lake. 

The term iron pitch is used to designate large and isolated masses 
of extremely hard asphaltum found both within and without the bor¬ 
ders of the lake. It is supposed to have been formed by the action of 
heat caused by forest fires, which, sweeping over the softer pitch, re¬ 
moved its more volatile constituents. 

The name epuree is given to asphaltum refined on the island of 
Trinidad. The process is conducted in a very crude manner, in large, 
open, cast-iron sugar boilers. 

The characteristics of crude Trinidad asphaltum, both lake and 
land, are as follows: It is composed of bitumen mixed with fine sand, 
clay, and vegetable matter. Its specific gravity varies according to the 
impurities present, but is usually about 1.28. Its color, when fleshly 
excavated, is a brown, which changes to black on exposure to the at¬ 
mosphere. When freshly broken, it emits the usual bituminous odor- 
It is porous, containing gas cavities, and in consistency resembles 
cheese. If left long enough in the sun, the surface will soften and melt, 
and will finally flow into a more or less compact mass. 

Refined Trinidad Asphaltum. The crude asphaltum is refined 
or purified by melting it in iron kettles or stills by the application of 
indirect - heat. 

The operation of refining proceeds as follows: During the heat¬ 
ing, the water and lighter oils are evaporated; the asphaltum is lique¬ 
fied ; the vegetable matter rises to the surface, and is skimmed off; the 
earthy and siliceous matters settle to the bottom; and the liquid asphal¬ 
tum is drawn off into old cement or flour barrels. 

When the asphaltum is refined without agitation, the residue 
remaining in the still forms a considerable percentage of the crude 
material, frequently amounting to 12 per cent; and it was at one time 
considered that the greater the amount of this residue the better the 




HIGHWAY CONSTRUCTION 


109 


quality of the refined asphaltum. Since agitation has been adopted, 
however, the greater part of the earthy and siliceous matters is retained 
in suspension; and it has come to be considered just as desirable for 
a part of the surface mixture as the sand which is subsequently added. 
The refined asphaltum, if for local use, is generally converted into 
cement in the same still in which it was refined. 

The average composition of both the land and lake varieties is 
shown by the following analyses: 

Average Composition of Trinidad Asphaltum 


Constituents 

% 

Lake 

Land 

Hard 

Soft 

Water . 

Per Cent 
27.85 
26.38 
7.63 
38.14 

Per Cent 
34.10 
25.05 

6.35 

34.50 

Per Cent 
26.62 

27.57 

8.05 

37.76 

Inorganic matter. 

Organic non-bituminous matter. 

Bitumen . . . 

When the analyses are calculated to a basis of dry 
substances, the composition is: Inorganic matter 
Organic matter not bitumen. 

100.00 

100.00 

100.00 

36.56 

10.57 
52.87 

38.00 

9.64 

52.36 

37.74 

10.68 

51.58 

Bitumen . 

The substances volatilized in 10 hou^s at 400° F ... 
The substances soften at . 

100.00 

100.00 

100.00 

3.66 
190° F. 
200° F. 

12.24 

170° F. 
185° F. 

0.86 to 1.37 
200° to 250° F. 
210° to 328° F. 

“ “ flow at. 



The characteristics of refined Trinidad asphaltum are as follows: 
The color is black, with a homogeneous appearance. At a tempera¬ 
ture of about 70° F., it is very brittle, and breaks with a conchoidal 
fracture. It burns with a yellowish-white flame, and in burning emits 
an empyreumatic odor, and possesses little cementitious quality. To 
give it the required plasticity and tenacity, it is mixed while liquid with 
from 16 to 21 pounds of residuum oil to 100 pounds of asphaltum. 

The product resulting from the combination is called asphalt 
paving-cement. Its consistency should be such that, at a temperature 
of from 70° to 80° F., it can be easily indented with the fingers, and on 
slight warming be drawn out in strings or threads. 

Artificial Asphalt Pavements. The pavements made from Trini¬ 
dad, Bermudez, California, and similar asphaltums, are composed of 
mechanical mixtures of asphaltic cement, sand, and stone-dust. 

The sand should be equal in quality to that used for hydraulic 
cement mortar; it must be entirely free from clay, loam, and vegetable 







































110 


HIGHWAY CONSTRUCTION 


impurities; its grains should be angular and range from coarse to fine. 

The stone-dust is used to aid in filling the voids in the sand and 
thus reduce the amount of cement. The amount used varies with the 
coarseness of the sand and the quality of the cement, and ranges from 
5 to 15 per cent. (The voids in sand vary from .3 to .5 per cent.) 

As to the quality of the stone-dust, that from any durable stone is 
equally suitable. Limestone-dust was originally used, and has never 
been entirely discarded. 

The paving composition is prepared by heating the mixed sand 
and stone-dust and the asphalt cement separately to a temperature of 
about 300° F. The heated ingredients are measured into a pug-mill 
and thoroughly incorporated. When this is accomplished, the mix¬ 
ture is ready for use. It is hauled to the street and spread with iron 
rakes to such depth as will give the required thickness when compacted 
(the finished thickness varies between lj and 2J inches). The re¬ 
duction of thickness by compression is generally about 40 per cent. 

The mixture is sometimes laid in two layers. The first is called 
the binder or cushion=coat; it contains from 2 to 5 per cent more cement 
than the surface-coat; its thickness is usually \ inch. The object of the 
binder course is to unite the surface mixture with the foundation, which 
it does through the larger percentage of cement that it contains, which, 
if put in the surface mixture, would render it too soft. 

The paving composition is compressed by means of rollers and 
tamping irons, the latter being heated in a fire contained in an iron 
basket mounted on wheels. These irons are used for tamping such 
portions as are inaccessible to the roller—namely, gutters, around man¬ 
hole heads, etc. 

Two rollers are sometimes employed; one, weighing 5 to 6 tons 
and of narrow tread, is used to give the first compression; and the 
other, weighing about 10 tons and of broad tread, is used for finishing. 
The amount of rolling varies; the average is about 1 hour per 1,000 
square yards of surface. After the primary compression, natural 
hydraulic or any impalpable mineral matter is sprinkled over the sur¬ 
face, to prevent the adhesion of the material to the roller and to give 
the surface a more pleasing appearance. When the asphalt is laid 
up to the curb, the surface of the portion forming the gutter is painted 
with a coat of hot cement. 

Although asphaltum is a bad conductor of heat, and the cement 




HIGHWAY CONSTRUCTION 


111 


retains its plasticity for several hours, occasions may and do arise 
through which the composition before it is spread has cooled; its con¬ 
dition when this happens is analogous to hydraulic cement which has 
taken a “set,” and the same rules which apply to hydraulic cement in 
this condition should be respected in regard to asphaltic cement. 

The proportions of the ingredients in the paving mixture are not 
constant, but vary with the climate of the place where the pavement 
is to be used, the character of the sand, and the amount and character 
of the traffic that will use the pavement. The range in the proportion 
is as follows: 

Formula for Asphaltic Paving Mixture 

Asphalt cement. 12 to 15 per cent. 

Sand.70 to 83 “ 

Stone-dust. 5 to 15 “ “ 

A cubic yard of the prepared material weighs about 4,500 pounds, and 
will lay the following amount of wearing-surface: 

2j inches thick.12 square yards. 

2 “ “ .18 “ 

1£ “ “ .27 “ 

One ton of refined asphaltum makes about 2,300 pounds of asphalt 
cement, equal to about 3.4 cubic yards of surface material. 

Foundation. A solid, unyielding foundation is indispensable 

with all asphaltic pavements, because asphalt of itself has no power of 

offering resistance to the action of traffic, consequently it is nearly 

always placed upon a bed of hydraulic cement concrete. The concrete 

must be thoroughly set and its surface dry before the asphalt is laid 

upon it; if not, the water will be sucked up and converted into steam, 

with the result that coherence of the asphaltic mixture is prevented, 

and, although its surface may be smooth, the mass is really honey- 

combed, so that as soon as the pavement is subjected to the action of 

traffic, the voids or fissures formed by the steam appear on the surface, 

and the whole pavement is quickly broken up. 

Advantages of Asphalt Pavement. These, may be summed up 
as follows: 

(1) Ease of traction. 

(2) It is comparatively noiseless under traffic. 

(3) It is impervious. 

(4) It is easily cleansed. 

(5) It produces neither mud nor dust. 

(6) It is pleasing to the eye. 











112 


HIGHWAY CONSTRUCTION 


(7) It suits all classes of traffic. 

(8) There is neither vibration nor concussion in traveling over it. 

(9) It is expeditiously laid, thereby causing little inconvenience 
to traffic. 

(10) Openings to gain access to underground pipes are easily 
made. 

(11) It is durable. 

(12) It is easily repaired. 

Defects of Asphalt Pavement. These are as follows: 

(1) It is slippery under certain conditions of the atmosphere. 
The American asphalts are much less so than the European, on account 
of their granular texture derived from the sand. The difference is 
very noticeable; the European are as smooth as glass, while the Ameri¬ 
can resemble fine sandpaper. 

(2) It will not stand constant moisture, and will disintegrate if 
excessively sprinkled. 

(3) Under extreme heat it is liable to become so soft that it will 
roll or creep under traffic and present a wavy surface; and under ex¬ 
treme cold there is danger that the surface will crack and become 
friable. 

(4) It is not adapted to grades steeper than 2k per cent, although 
it is in use on grades up to 7.30 per cent. 

(5) Repairs must be quickly made, for the material has little 
coherence, and if, from irregular settlement of foundation or local vio¬ 
lence, a break occurs, the passing wheels rapidly shear off the sides of 
the hole, and it soon assumes formidable dimensions. 

The strewing of sand upon asphalt renders it less slippery; but in 
addition to the interference of the traffic while this is being done, there 
are further objections—namely, the possible injury by the sand cutting 
into the asphalt, the expense of labor and materials, and the mud 
formed, which has afterwards to be removed. 

Although pure asphaltum is absolutely impervious and insoluble 
in either fresh or salt water, yet asphalt pavements in the continued 
presence of water are quickly disintegrated. Ordinary rain or daily 
sprinkling does not injure them when they are allowed to become per¬ 
fectly dry again. The damage is most apparent in gutters and adja¬ 
cent to overflowing drinking fountains. This defect has long been 
recognized; and various measures have been taken to overcome it, or 




HIGHWAY CONSTRUCTION 


113 


at least to reduce it to a minimum. In some cities, ordinances have 
been passed, seeking to regulate the sprinkling of the streets; and in 
many places the gutters are laid with stone or vitrified brick (see Figs. 


Granite Curb 



Asphalt 


sand- 

T7 

\:pGrquel^\ 



Fig. 64. 

64 and 65), while in others the asphalt is laid to the curb, a space of 
12 to 15 inches along the curb being covered with a thin coating of 
asphalt cement. 

Asphalt laid adjoining center-bearing street-car rails is quickly 
broken down and destroyed. This defect is not peculiar to asphalt. 
All other materials when placed in similar positions are quickly worn. 
Granite blocks laid along such tracks have been cut into at a rate of 
more than half an inch a year. The frequent entering and turning off 
of vehicles from car tracks is one of the severest tests that can be 



Fig. 65. 

applied to any paving material; moreover, the gauge of trucks and 
vehicles is frequently greater than that of the rails, so one wheel runs 
on the rail and the other outside. The number of wheels thus travel¬ 
ing in one line must quickly wear a rut in any material adjoining the 
center-bearing rail. 

To obviate the destruction of asphalt in such situations, it is usual 
to lay a strip of granite block or brick paving along the rail. This 
pavement should be of sufficient width to support the wheels of the 
widest gauge using the street. 






























































114 


HIGHWAY CONSTRUCTION 


The burning of leaves or making of fires on asphalt pavements 
should not be permitted, as it injures the asphalt, and the paving com¬ 
panies cannot be compelled to repair the damaged places without 
compensation. 

Asphalt Blocks. Asphalt paving blocks are formed from a mix¬ 
ture of asphaltic cement and crushed stone in the proportion of 8 to 12 
per cent of cement to 88 and 92 per cent of stone. The materials are 
heated to a temperature of about 300° F., and mixed while hot in a 
suitable vessel. When the mixing is complete, the material is placed 
in moulds and subjected to heavy pressure, after which the blocks are 
cooled suddenly by plunging into cold water. 

The usual dimensions of the blocks are 4 inches wide, 3 inches 
deep, and 12 inches long. 

Foundation. The blocks are usually laid upon a concrete founda¬ 
tion with a cushion-coat of sand about J inch thick. They are laid 
with their length at right angles to the axis of the street, and the longitu¬ 
dinal joints should be broken by a lap of at least 4 inches. The blocks 
are then either rammed with hand rammers oi rolled with a light steam 
roller, the surface being covered with clean, fine sand; no joint filling is 
used, as, under the action of the sun and traffic, the blocks soon become 
cemented. 

The advantages claimed for a pavement of asphalt blocks over a 
continuous sheet of asphalt are: (1) That they can be made at a 
factory located near the materials, whence they can be transported to 
the place where they are to be used and can be laid by ordinary paviors, 
whereas sheet pavements require special machinery and skilled labor; 

(2) that they are less slippery, owing to the joints and the rougher 
surface due to the use of crushed stone. 

Asphalt Macadam—Bituminous Macadam. Recently it has been 
proposed to use asphalt as a binding material for broken stone. 
There are two patented processes—the Whinery and the Warren— 
which differ slightly in, details. 

The advantages claimed for these methods are: (1) The first 
coat will be materially less; (2) it will offer a better foothold for horses; 

(3) it will be at least as durable as the ordinary sheet asphalt; (4) it will 
not shift under traffic and roll into waves; (5) it will not crack; (6) it 





HIGHWAY CONSTRUCTION 


115 


can be repaired more cheaply and with less skilled labor than can the 
ordinary sheet asphalt. 

Tools Employed in Construction of Asphalt Pavements. The 



Fig. 67. Asphalt Tools. 


tools used in laying sheet asphalt pavements comprise iron rakes; 
hand rammers; smoothing irons (Fig. 67); pouring pots (Fig. 69); 

















































116 


HIGHWAY CONSTRUCTION 


hand rollers, either with or without a fire-pot (Fig. 68); and steam 
rollers, with or without provision for heating the front roll (Fig. 66). 
These rollers are different in construction, appearance, and weight 



Fig. 68. Hand Hollers. 



from those employed for compacting broken stone. The difference 
is due to the different character of the work required. 

The principal dimensions of a five-ton roller are as follows: 


Front roll or steering-wheel 
Rear roll or driving-wheel. 
Width of front roll. 


Extreme length 
“ height. 
Water capacity. 
Coal 


30 to 32 inches diameter. 
48 

40 “ 

40 “ “ 

. 14 feet. 

. 7 to 8 feet. 

.80 to 100 gallons. 

. 200 pounds. 
























































HIGHWAY CONSTRUCTION 


117 


FOOTPATHS—CURBS—GUTTERS. 

A footpath or walk is simply a road under another name—a road 
for pedestrians instead of one for horses and vehicles. The only 
difference that exists is in the degree of service required; but the con¬ 
ditions of consruction that render a road well adapted to its object are 
very much the same as those required for a walk. 

The effects of heavy loads such as use carriageways are not felt 
upon footpaths; but the destructive action of water and frost is the 
same in either case, and the treatment to counteract or resist these 
elements as far as practicable, and to produce permanency, must be 
the controlling idea in each case, and should be carried out upon a 
common principle. It is not less essential that a walk should be well 
adapted to its object than that a road should be; and it is annoying to 
find it impassable or insecure and in-want of repair when it is needed 
for convenience or pleasure. In point of economy, there is the same 
advantage in constructing a footway skilfully and durably as there is 
in the case of a road. 

Width. The width of footwalks (exclusive of the space occupied 
by projections and shade trees) should be ample to accomodate com¬ 
fortably the number of people using them. In streets devoted entirely 
to commercial purposes, the clear width should be at least one-third 
the width of the carriageway; in residential and suburban streets, a 
very pleasing result can be obtained by making the walk one-half the 
width of the roadway, and devoting the greater part to grass and shade 
trees. 

Cross Slope. The surface of footpaths must be sloped so that 
the surface water will readily flow to the gutters. This slope need not 
be very great; ^ inch per foot will be sufficient. A greater slope with a 
thin coating of ice upon it, becomes dangerous to pedestrians. 

Foundation. As in the case of roadways, so with footpaths, the 
foundation is of primary importance. Whatever material may be used 
for the surface, if the foundation is weak and yielding, the surface will 
settle irregularly and become extremely objectionable, if not danger¬ 
ous, to pedestrians. 

Surface. The requirements of a good covering for sidewalks are: 

(1) It must be smooth but not slippery. 

(2) It must absorb the minimum amount of water, so that it 
may dry rapidly after rain. 





118 


HIGHWAY CONSTRUCTION 


(3) It must not be easily abraded. 

(4) It must be of uniform quality throughout, so that it may 
wear evenly. 

(5) It must neither scale nor flake. 

(6) Its texture must be such that dust will not adhere to it. 

(7) It must be durable. 

Materials. The materials used for footpaths are as follows: 
Stone, natural and artificial; wood; asphalt; brick; tar concrete; and 
gravel. 

Of the natural stones, sandstone (bluestone) and granite are ex¬ 
tensively employed. 

The bluestone, when well laid, forms an excellent paving material. 
It is of compact texture, absorbs water to a very limited extent, and 
hence soon dries after rain; it has sufficient hardness to resist abrasion, 
and wears well without becoming excessively slippery. 

Granite, although exceedingly durable, wears very slippery, and 
its surface has to be frequently roughened. 

Slabs, of whatever stone, must be of equal thickness throughout 


their entire area; the 



whole thickness (edges 
must not be left feather¬ 


ed as shown in Fig. 70); and the slabs must be solidly bedded on the 
foundation and the joints filled with cement-mortar. 

Badly set or faultily dressed flagstones are very unpleasant to 
walk over, especially in rainy weather; the unevenness causes pedes¬ 
trians to stumble, and rocking stones squirt dirty water over their 
clothes. 

Wood has been largely used in the form of planks; it is cheap in 
first cost, but proves very expensive from the fact that it lasts but a 
comparatively short time and requires constant repair to keep it 
from becoming darfgerous. 

Asphalt forms an excellent footway pavement; it is durable and 
does not wear slippery. 

Brick. Brick of suitable quality, well and carefully laid on a 
concrete foundation, makes an excellent footway pavement for resi- 






HIGHWAY CONSTRUCTION 


no 


dential and suburban streets of large cities, and also for the main 
streets of smaller towns. The bricks should be a good quality of 
paving brick (ordinary building brick are unsuitable, as they soon 
wear out and are easily broken). The bricks should be laid in parallel 
rows on their edges, with their length at right angles to the axis of the 
path. 

Curbstones. Curbstones are employed for the outer side of foot¬ 
ways, to sustain the coverings and form the gutter. Their upper edges 
are set flush with the footwalk pavement, so that the water can flow 
over them into the gutters. 

The disturbing forces which the curb has to resist, are : (1) The 
pressure of the earth behind it, which is frequently augmented by 
piles of merchandise, building materials, etc. This pressure tends to 
overturn it, break it transversely, or move it bodily on its base. (2) 
The pressure due to the expansion of freezing earth behind and be¬ 
neath it. This force is most frequent where the sidewalk is partly 
sodded and the ground is accordingly moist. Successive freezing and 
thawing of the earth behind the curb will occasion a succession of 
thrusts forward, which, if the curb be of faulty design, will cause it to 
incline several degrees from the vertical. (3) The concussions and 
abrasions caused by traffic To withstand the destructive effect of 
wheels, curbs are faced with iron; and a concrete curb with a rounded 
edge of steel has been patented and used to some extent. Fires built 
in the gutters deface and seriously injure the curb. Posts and trees 
set too near the curb, tend to break, displace, and destroy it. 

The use of drain tiles under the curb is a subject of much differ¬ 
ence of opinion among engineers. Where the subsoil contains water 
naturally, or is likely to receive it from outside the curb-lines, the use 
of drains is of decided benefit; but great care must be exercised in 
jointing the drain-tiles, lest the soil shall be loosened and removed, 
causing the curb to drop out of alignment. 

The materials employed for curbing are the natural stones, as 
granite, sandstone (bluestone), etc., artificial stone, fire-clay, and cast 
iron. 

The dimensions of curbstones vary considerably in different 
localities and according to the width of the footpaths; the wider the 
path, the wider should be the curb. It should, however, never be less 
than 8 inches deep, nor narrower than 4 inches. Depth is necessary 




120 


HIGHWAY CONSTRUCTION 


to prevent the curb turning over toward the gutter. It should never 
be in smaller lengths than 3 feet. The top surface should be beveled 
off to conform to the slope of the footpath. The front face should be 
hammer-dressed for a depth of about 6 inches, in order that there may 
be a smooth surface visible against the gutter. The back for 3 inches 



Fig. 71. 


from the top should also be dressed, so that the flagging or other paving 
may butt fair against it. The end joints should be cut truly square, 
the full thickness of the stone at the top, and so much below the top as 
will be exposed, the remaining portion of the depth and bottom should 
be roughly squared, and the bottom should be fairly parallel to the 
top. (See Figs. 71 and 72). 

Artificial Stone. Artificial stone is being extensively used as a 



footway paving material. Its manufacture is the subject of several 
patents, and numerous kinds are to be had in the market. When 
manufactured of first-class materials and laid in a substantial manner, 
with proper provision against the action of frost, artificial stone forms 
a durable, agreeable, and inexpensive pavement. 












































HIGHWAY CONSTRUCTION 


121 



Fig. 73. Tamper. 


ihe varieties most extensively used in the United States are 
known by the names of granolithic, monolithic , jerrolithic, kosmocrete, 
metalithic, etc. 

The process of manufacture is practically the same for all kinds, 

the difference being in the materials em¬ 
ployed. The usual ingredients are Port¬ 
land cement, sand, gravel, and crushed 
stone. 

Artificial stone for footway pave¬ 
ments is formed in two ways—namely, 
in blocks manufactured at a factory, 
brought on the ground, and laid in the 
same manner as natural stone; or the raw 
materials are brought upon the work, pre¬ 
pared, and laid in place, blocks being formed by the use of board 
moulds. 

The manner of laying is practically the same for all kinds. The 
area to be paved is excavated to a mini¬ 
mum depth of 8 inches, and to such great¬ 
er depths as the nature of the ground may 
require to secure a solid foundation. The 
surface of the ground so exposed is well 
compacted by ramming; and a layer of 
gravel, ashes, clinker, or other suitable material is spread and consoli¬ 
dated; on this is placed the concrete wearing surface, usually 4 inches 

thick. As a protection against the lifting 
effects of frost, the concrete is laid in 
squares, rectangles, or other forms hav¬ 
ing areas ranging from 6 to 30 square 
feet, strips of w T ood being employed to 
form moulds in which the concrete is 
placed. After the concrete is set, these strips are removed, leaving 
joints about half an inch wide between the blocks. Under some 
patents these joints are filled with cement; under others, with tarred 
paper; and in some cases they are left open. 

Tools Employed in Construction of Artificial Stone Pavements. 
Tampers (Fig. 73). Cast iron, with hickory handle; range from 6 
by 8 inches to 8 by 10 inches. 



Fig. 74. Quarter-Round. 



Fig. 75. Jointer. 















122 


HIGHWAY CONSTRUCTION 


Quarter-Round, (Fig. 74). 
for forming corners and edges. 



Made of any desired radius. Used 

Jointer (Fig. 75). Used for 
trimming and finishing the joints. 

Cutter (Fig. 7G). Used for cut¬ 
ting the concrete into blocks. 

Gutter Tool (Fig. 77). Used 
for forming and finishing gutters. 

Imprint Rollers (Figs. 78 and 
79). Here are shown two designs 
of rollers for imprinting the surface 
of artificial stone pavements with 
grooves, etc. 


SELECTING THE PAVEMENT 


The problem of selecting the best pavement for any particular 
case is a local one, not only for each city, but also for each of the various 
parts into which the city is imperceptibly divided; and it involves so 
many elements that the nicest balancing of the relative values for each 
kind of pavement is required, to arrive at a correct conclusion. 

In some localities, the proximity of one or more paving materials 
determines the character of the pavement; 
while in other cases a careful investigation 
may be required in order to select the 
most suitable material. Local conditions 
should always be considered; hence it is 
not possible to lay down any fixed rule as to what material makes the 
best pavement. 

The qualities essential to a good pavement may be stated as 
follows: 



Fig. 77. Gutter Tool. 


(1) It should be impervious. 

(2) It should afford good foothold for horses. 

(3) It should be hard and durable, so as to resist wear and dis¬ 
integration. 

(4) It should be adapted to every grade. 

(5) It should suit every class of traffic. 

(6) It should offer the minimum resistance to traction. 

(7) It should be noiseless. 

(8) It should yield neither dust nor mud. 














HIGHWAY CONSTRUCTION 


123 




(9) It should be easily cleaned. 

(10) It should be cheap. 

Interests Affected in Selection. Of the above requirements, 
numbers 2, 4, 5, and 6 affect the traffic and determine the cost of haul¬ 
age by the limitations of loads, speed, 
and wear and tear of horses and ve¬ 
hicles. If the surface is rough or the 
foothold bad, the weight of the load 
a horse can draw is decreased, thus ne¬ 
cessitating the making of more trips or 
the employment of more horses and 
vehicles to move a given weight. A 
defective surface necessitates a reduc¬ 
tion in the speed of movement and 
consequent loss of time; it increases the 
wear of horses, thus decreasing their 

Fig. 78. imprint Roller. life service and lessening the value of 

their current services; it also, increases 
the cost of maintaining vehicles and 
harness. 

Numbers 7, 8, and 9 affect the 
occupiers of adjacent premises, who 
suffer from the effect of dust and 
noise; they also affect the owners of 
said premises, whose income from 
rents is diminished where these disad¬ 
vantages exist. Numbers 3 and 10 af¬ 
fect the taxpayers alone—first, as to 
the length of time during which the 
covering remains serviceable; and sec¬ 
ond, as to the amount of the annual 

repairs. Number 1 affects the adjacent occupiers principally on 
hygienic grounds. Numbers 7 and 8 affect both traffic and occupiers. 

Problem Involved in Selection. The problem involved in the 
selection of the most suitable pavement consists of the following 
factors: (1) adaptability; (2) desirability; (3) serviceability; (4) dura¬ 
bility; (5) cost. 

Adaptability. The best pavement for any given roadway will 


Fig. 79. Imprint Roller. 










124 


HIGHWAY CONSTRUCTION 


depend altogether on local circumstances. Pavements must be adapt¬ 
ed to the class of traffic that will use them. The pavement suitable 
for a road through an agricultural district will not be suitable for the 
streets of a manufacturing center; nor will the covering suitable for 
heavy traffic be suitable for a pleasure drive or for a residential district. 

General experience indicates the relative fitness of the several 
materials as follows: 

For country roads, suburban streets, and pleasure drives—broken 
stone. For streets having heavy and constant traffic—rectangular 
blocks of stone, laid on a concrete foundation, with the joints filled 
with bituminous or Portland cement grout. For streets devoted to 
retail trade, and where comparative noiselessness is essential—asphalt, 
wood, or brick. 

Desirability, The desirability of a pavement is its possession of 
qualities which make it satisfactory to the people using and seeing it. 
Between two pavements alike in cost and durability, people will have 
preferences arising from the condition of their health, presonal pre¬ 
judices, and various other intangible influences, causing them to select 
one rather than the other in their respective streets. Such selections 
are often made against the demonstrated economies of the case, and 
usually in ignorance of them. Whenever one kind of pavement is 
more economical and satisfactory to use than is any other, there should 
not be any difference of opinion about securing it, either as a new 
pavement or in the replacement of an old one. 

The economic desirability of pavements is governed by the ease 
of movement over them, and is measured by the number of horses or 
pounds of tractive force required to move a given weight—usually one 
ton—over them. The resistance offered to traction by different pave¬ 
ments is shown in the following table: 

O 

Resistance to Traction on Different Pavements 


Kind of Pavement 

Tractive Resistance 


Pounds per ton 

In terms of the load 

Asphalt (sheet). 

30 to 70 

1 to 1 

6 7 10 3 0" 

Brick. 

15 “ 40 

1 “ 1 

1 3 3 5 O' 

Cobblestones. 

50 “ 100 

1 “ 1 

To To 

Stone-block. 

30 “ 80 

1 “ 1 

17 TF 

Wood-block rectangular 

30 “ 50 

1 “ 1 

15 7 To 

Wood-block round. 

40 “ 80 

1 “ 1 

TO TF 



























HIGHWAY CONSTRUCTION 


125 


Serviceability. The serviceability of a pavement is its quality of 
fitness for use. This quality is measured by the expense caused to the 
traffic using it—namely, the wear and tear of horses and vehicles, loss 
of time, etc. No statistics are available from which to deduce the 
actual cost of wear and tear. 

The serviceability of any pavement depends in great measure 
upon the amount of foothold afforded by it to the horses—provided, 
however, that its surface be not so rough as to absorb too large a per¬ 
centage of the tractive energy required to move a given load over it. 
Cobblestones afford excellent foothold, and for this reason are largely 
employed by horse-car companies for paving between the rails; but 
the resistance of their surface to motion requires the expenditure ot 
about 40 pounds of tractive energy to move a load of 1 ton. Asphalt 
affords the least foothold; but the tractive force required to overcome 
the resistance it offers to motion is only about 30 pounds per ton. 

Comparative Safety. The comparison of pavements in respect of 
safety, is the average distance traveled before a horse falls. The 
materials affording the best foothold for horses are as follows, stated 
in the order of their merit: 

(1) Earth, dry and compact. 

(2) Gravel. 

(3) Broken stone (macadam). 

(4) Wood. 

(5) Sandstone and brick. 

(G) Asphalt. 

(7) Granite blocks. 

Durability. The durability of pavement is that quality which 
determines the length of time during which it is serviceable, and does 
not relate to the length of time it has been down. The only measure 
of durability of a pavement u the amount of traffic tonnage it will bear 
before it becomes so worn that the cost of replacing it is less than the 
expense incurred by its use. 

As a pavement is a construction, it necessarily follows that there 
is a vast difference between the durability of the pavement and the 
durability of the materials of which it is made. Iron is eminently 
durable; but, as a paving material, it is a failure. 

Durability and Dirt. The durability of a paving material will 
vary considerably with the condition of cleanliness observed. One 




126 


HIGHWAY CONSTRUCTION 


inch of overlying dirt will most effectually protect the pavement from 
abrasion, and indefinitely prolong its life. But the dirt is expensive, 
it injures apparel and merchandise, and is the cause of sickness and 
discomfort. In the comparison of different pavements, no traffic 
should be credited to the dirty one. - 

Life of Pavements. The life or durability of different pavements 
under like conditions of traffic and maintenance, may be taken as 
follows: 

Life Terms of Various Pavements 


Material 

Life Term 

Granite block. 

Sandstone. 

Asphalt..... 

12 to 30 years 

6 “ 12 “ 

10 “ 14 “ 

W ood . 

3 “ 7 “ 

Limestone ... 

1 “ 3 “ 

Brick . 

5 “ ? “ 

Macadam. 

5 “ 9 “ 


Cost. The question of cost is the one which usually interests 
taxpayers, and is probably the greatest stumbling-block in the attain¬ 
ment of good roadways. The first cost is usually charged against the 
property abutting on the highway to be improved. The result is that 
the average property owner is always anxious for a pavement that costs 
little, because he must pay for it, not caring for the fact that cheap 
pavements soon wear out and become a source of endless annoyance 
and expense. Thus false ideas of economy always have stood, and 
undoubtedly to some extent always will stand, in the way of realizing 
that the best is the cheapest. 

The pavement which has cost the most is not always the best; nor 
is that which cost the least the cheapest; the one which is truly the cheap¬ 
est is the one vdiich makes the most profitable returns in proportion to the 
amount expended upon it. No doubt there is a limit of cost to go be¬ 
yond which would produce no practical benefit; but it will always be 
found more economical to spend enough to secure the best results, and 
this will always cost less in the long run. One dollar well spent is 
many times more effective than one-lialf the amount injudiciously 
expended in the hopeless effort to reach sufficiently good results. The 
cheaper work may look as well as the more expensive for the 
time, but may very soon have to be done over again. 

Economical Benefit. The economic benefit of a good roadway is 


























HIGHWAY CONSTRUCTION 


127 


comprised in its cheaper maintenance; the greater facility it offers for 
traveling, thus reducing the cost of transportation; the lower cost of 
repairs to vehicles, and less wear of horses, thus increasing their term 
of serviceability and enhancing the value of their present service; the 
saving of time; and the ease and comfort afforded to those using the 
roadway. 

First Cost. The cost of construction is largely controlled by the 
locality of the place, its proximity to the particular material used, and 
the character of the foundation. 

The Relative Economies of Pavements—whether of the same 
kind in different condition, or of different kinds in like good condition 
—are sufficiently determined by summing their cost under the following 
headings of account: 

(1) Annual interest upon first cost. 

(2) Annual expense for maintenance. 

(3) Annual cost for cleaning and sprinkling. 

(4) Annual cost for service and use. 

(5) Annual cost for consequential damages. 

Interest on First Cost. The first cost of a pavement, like any 
other permanent investment, is measurable for purposes of comparison 
by the amount of annual interest on the sum expended. Thus, assum¬ 
ing the worth of money to be 4%, a pavement costing $4 per square 
yard entails an annual interest loss or tax of $0.10 per square yard. 

Cost of Maintenance. Under this head must be included all out¬ 
lays for repairs and renewals which are made from the time when the 
pavement is new and at its best to a time subsequent, when, by any 
treatment, it is again put in equally good condition. The gross sum 
so derived, divided by the number of years which elapse between the 
two dates, gives an average annual cost for maintenance. 

Maintenance means the keeping of the pavement in a condition 
practically as good as when first laid. The cost will vary considerably 
depending not only upon the material and the manner in which it is 
constructed, but upon the condition of cleanliness observed, and the 
quantity and quality of the traffic using the pavement. 

The prevailing opinion that no pavement is a good one unless, 
when once laid, it will take care of itself, is erroneous; there is no such 
pavement. All pavements are being constantly worn by traffic and 
by the action of the atmosphere; and if any defects which appear are 





128 


HIGHWAY CONSTRUCTION 


not quickly repaired, the pavements soon become unsatisfactory and 
are destroyed. To keep them in good repair, incessant attention is 
necessary, and is consistent with economy. \ T et claims are made that 
particular pavements cost little or nothing for repairs, simply because 
repairs in these cases are not made, while any one can see the need of 
them. 

Cost of Cleaning and Sprinkling. Any pavement, to be con¬ 
sidered as properly cared for, must be kept dustless and clean. While 
circumstances legitimately determine in many cases that streets must 
be cleaned at daily, weekly, or semi-weekly intervals, the only admis¬ 
sible condition for the purpose of analysis of street expenses must be 
that of like requirements in both or all cases subjected to comparison. 

The cleaning of pavements, as regards both efficiency and cost, 
depends (1) upon the character of the surface; (2) upon the nature of 
the materials of which the pavements are composed. Block pave¬ 
ments present the greatest difficulty; the joints can never be perfectly 
cleaned. The order of merit as regards facility of cleansing, is: (1) 
asphalt, (2) brick, (3) stone, (4) wood, (5) macadam. 

Cost of Service and Use. The annual cost for service is made up 
by combining several items of cost incidental to the use of the pave¬ 
ment for traffic—for instance, the limitation of the speed of movement, 
as in cases where a bad pavement causes slow driving and consequent 
loss of time; or cases where the condition of a pavement limits the 
weight of the load which a horse can haul, and so compels the making 
of more trips or the employment of more horses and vehicles; or cases 
where conditions are such as to cause greater wear and tear of vehicles, 
of equipage, and of horses. If a vehicle is run 1,500 miles in a year, 
and its maintenance costs $30 a year, then the cost of its maintenance 
per mile traveled is two cents. If the value of a team’s time is, say, 
$1 for the legitimate time taken in going one mile with a load, and in 
consequence of bad roads it takes double that time, then the cost to 
traffic from having to use that one mile of bad roadway is $1 for each 
load. The’same reasoning applies to circumstances where the weight 
of the load has to be reduced so as to necessitate the making of more 
than one trip. Again, bad pavements lessen not only the life-service 
of horses, but also the value of their current service. 

Cost for Consequential Damages. The determination of conse¬ 
quential damages arising from the use of defective or unsuitable pave- 








HIGHWAY CONSTRUCTION 


129 


merits, involves the consideration of a wide array of diverse circum¬ 
stances. Rough-surfaced pavements, when in their best condition, 
afford a lodgment for organic matter composed largely of the urine 
and excrement of the animals employed upon the roadway. In 
warm and damp weather, these matters undergo putrefactive fer¬ 
mentation, and become the most efficient agency for generating and 
disseminating noxious vapors and disease germs, now recognized as 
the cause of a laige part of the ills afflicting mankind. Pavements 
formed of porous materials are objectionable on the same, if not even 
stronger, grounds. 

Pavements productive of dust and mud are objectionable, and 
especially so on streets devoted to retail trade. If this particular 
disadvantage be appraised at so small a sum per lineal foot of frontage 
as SI.50 per month, or six cents per day, it exceeds the cost of the best 
quality of pavement free from these disadvantages. 

Rough-surfaced pavements are noisy under traffic and insufferable 
to nervous invalids, and much nervous sickness is attributable to them. 
To all persons interested in nervous invalids, this damage from noisy 
pavements is rated as being far greater than would be the cost of sub¬ 
stituting the best quality of noiseless pavement; but there are, under 
many circumstances, specific financial losses, measurable in dollars 
and cents, dependent upon the use of rough, noisy pavements. They 
reduce the rental value of buildings and offices situated upon streets 
so paved—offices devoted to pursuits wherein exhausting brain work 
is required. In such locations, quietness is almost indispensable, 
and no question about the cost of a noiseless pavement weighs against 
its possession. When an investigator has done the best he can to 
determine such a summary of costs of a pavement, he may divide the 
amount of annual tonnage of the street traffic by the amount of annual 
costs, and know what number of tons of traffic are borne for each cent 
of the average annual cost, which is the crucial test for any comparison, 
as follows: 

(1) Annual interest upon first cost.S 

(2) Average annual expense for maintenance and renewal... 

(3) Annual cost for custody (sprinkling and cleaning). 

(4) Annual cost for service and use. 

(5) Annual cost for consequential damages. 

Amount of average annual cost. 

Annual tonnage of traffic. 

Tons of traffic for each cent of cost. 

Gross Cost of Pavements. Since the cost of a pavement depends 











130 


HIGHWAY CONSTRUCTION 


upon the material of which it is formed, the width of the roadway, the 
extent and nature of the traffic, and the condition of repair and clean¬ 
liness in which it is maintained, it follows that in no two streets is the 
endurance or the cost the same, and the difference between the highest 
and lowest periods of endurance and amount of cost is very con¬ 
siderable. 

The comparative cost of the various street pavements, including 
interest on first cost, sinking fund, maintenance, and cleaning, when 
reduced to a uniform standard traffic of 100,000 tons per annum for 
each yard in width of the carriageway, is about as follows: 


Comparative Cost of Various Pavements 


MATERIAL 

ANNUAL COST 
PER SQ. YD. 

Granite blocks 

$0.25 

Asphalt street 

OGO 

Brick 

0.35 

Wood. 

0.50 

















INDEX 


Absorption test for paving brick. 

Alignment of a road. 

Artificial asphalt pavements. 

Artificial stone. 

Asphalt blocks. 

Asphalt macadam. 

Asphalt pavements. 

advantages of. 

artificial. 

defects of. 

foundation for. 

tools employed in construction of 

Asphaltic paving materials. 

bituminous limest one. 

bituminous sandstones. 

Trinidad asphaltum. 

Asphaltic paving mixture, formula for 

Axle friction. 

Belgian block pavement. 

Bituminous cement for joint filling. 

Bituminous limetsone. 

Bituminous sandstones. 

Brick pavements. 

advantages of. 

defects of... 

foundation for. 

joint filling. 

manner of laying. 

sand cushion. 

Bridge sites. 

Broken stone roads. 

binding. 

compacting the broken stone. 

foundation for. 

size of stones. 

spreading the stone. 

thickness of broken stone. 

watering. 

Carts. 

Catch-basins. 


Page 

93 

23 

109 

120 

114 

114 
106 
111 
109 
112 
111 

115 
106 
106 
107 
107 
111 

10 

84 

89 

106 

107 

92 

95 

95 

95 
98 

96 
96 
17 
66 
70 
72 

69 
68 

70 
68 
70 
57 
79 


w 












































m 


INDEX 


Page 

City streets... 73 

arrangement of... 73 

catch-basins... 79- 

clrainage of. 78 

grades.. 74 

gutters. 79 

width of. 73 

Cobblestone pavement.'. 84 

Concrete foundation.,. 81 

Concrete-mixing machine. 100 

Construction profile. 24 

Country roads.».. 1 

location of. 12 

Covering of slopes. 46 

Creosoting. 103 

Cross-breaking test for paving brick. 94 

Cross levels. 17 

Crushing test for paving brick. 94 

Culverts.,. 38 

materials for. 41 

Curbstones. 119 

Determination of gradients. 25 

Drainage.....32, 36 

Draining tools. 63 

Drains, fall of. 35 

Dump cars. 58 

Dump wagons. 59 

‘ Earth. 47 

Earth roads. 50 

Earthenware pipe culverts. 42 

Earthwork. 44 

balancing cuts and fills. 44 

classification of. 47 

prosecution of.:.. 48 

✓ 

shrinkage of. 46 

side slopes. 45 

Embankments. 48 

Epuree. 108 

Fall of drains. 35 

Footpaths 

cross slope. 117 

foundation for. 117 

materials used for. 118 

surface. 117 

width of. 117 

Formation of embankments. 48 

Formula for asphaltic paving mixture. Ill 

Foundations. 80 


















































INDEX -133 


Page 

Foundations 

concrete. 81 

Friction. 1 

Grade, establishing. 28 

Gradient.6, 25 

Granite. 83 

Granite block pavement. 84 

advantages. 85 

blocks. 86 

cushion coat. 88 

defects. 85 

foundation for. 88 

joint filling.. 89 

ramming. 89 

Gravel. 65 

Gravel heaters. 101 

Gravel roads. 64 

repair of. 66 

Gutters. 79 

Halting places on mountain roads. 22 

Hardpan. 47 

Horse rollers. 63 

Inclination of side slopes. 45 

Iron pipe culverts. 43 

Level stretches. 28 

Levels. 16 

Location of country roads. 12 

bridge sites. 17 

cases to be treated. 18 

construction profile.. 24 

cross levels. 17 

final location. 24 

final selection. 17 

gradient. 25 

intermediate towns. j 20 

level stretches. 28 

levels. Id 

map. 16 

memoir. 16 

mountain roads. 21 

profile. 17 

reconnoissance. 12 

topography. 15 

Loose rock. 47 

Loss of height on mountain road. 22 

Loss of tractive power on inclines. 8 

Map. 16 

Maximum grade. 25 


















































134 


INDEX 


Page 


Mechanical graders. 59 

Melting furnaces. 101 

Memoir. 16 

Minimum grade. 27 

Mountain roads. 21 

halting places on. 22 


loss of height 
water on.... 
Pavements 


adaptability... 123 

comparative safety. 125 

cost. 126 

desirability. 124 

durability. 125 

economical benefit. 126 

life of. 126 

selecting. 122 

serviceability. 125 

Paving bricks 

properties of. 95 

tests of. 92 

absorption. 93 

cross-breaking. 94 

crushing. 94 

rattler. 92 

Picks. 53 

- Ploughs. 53 

Profile. 17 

Rattler test for paving brick. 92 

Reconnoissance. 12 

Refined Trinidad asphaltum. 108 

Resistance of the air. 11 

Resistance due to gravity on different inclinations. 5 

Resistance offered by roadway. 1 

friction. 1 

grade resistance. 6 

resistance to rolling. 2 

Road coverings. 64 

Road machines. 61 

Roads 

country. 1 

object of. 1 

width of. 29 

Roadways on rock slopes. 50 

Sand roads. 52 

Sandstones. 83 

Scrapers. 55 

Shovels. 53 

















































INDEX 


135 


Shrinkage of earthwork. 

Side ditches. 

Side slopes. 

Solid rock.. 

Springs, effect of on vehicles... 

Sprinkling carts. 

Steam rollers. 

Stone block pavements.•.:. 

Stone pavement on steep grades. .. 

Street grades. 

Sub-foundation drainage of streets. 

Surface drainage. 

Surface graders. 

Tables 

force required to draw loaded vehicles ove r inclined roads . 

grades, effects of upon load horse can draw on different pavements.. 

grades, method of designating.. 

pavements, cost of various. 

pavements, life terms of various... 

paving materials, proportions for. 

resistance to traction on different pavements. 

resistance to traction on different road surfaces.. 

specific gravity, weight, resistance to crushing, and absorptive 

power of stones. 

traction power of horses at different velocities. 

Trinidad asphaltum, average composition of. 

wood paving blocks, expansion of. 

Tests of paving brick. 

Tools employed in construction of artificial stone pavements. 

Tools employed in construction of block pavements.. 

Tools for grading.. 

carts. 

draining tools. 

dump cars. 

dump wagons. 

horse rollers... 

mechanical graders. 

picks. 

ploughs. 

road machines. 

scrapers. 

shovels. 

sprinkling carts.. 

surface graders.. 

wheelbarrows. 

Topography. 

Tractive power. 

Tractive power on inclines, loss of. 


Page 

46 
35 
45 

47 
11 
64 
72 
82 
91 
74 

78 

79 
61 

10 

8 

25 

130 

126 

31 

124 


84 

7 

109 

105 

92 

121 

100 

53 

57 
63 

58 

59 

63 
59 
53 
53 
61 

55 
53 

64 
61 

56 
15 

6 

8 


i 

















































136 


INDEX 


Page 

Transverse contour...30, 78 

Transverse grade. 77 

Trap rock. 83 

Trinidad asphaltum. 107 

Undulating grades. 27 

Vehicles, effect of springs on. 11 

Water on mountain roads. 22 

Water breaks. 37 

Wheelbarrows. 56 

Width of road. 29 

Wood pavements..!. 101 

advantages. 102 

chemical treatment of wood. 103 

creosoting.-. t . 103 

defects. 103 

expansion of blocks. 105 

filling for joints. 10G 

manner of laying. 105 

quality of wood. 103 

Zigzags. 24 






























































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































